It has been widely observed -- and often lamented -- that the design of 4th-edition Dungeons & Dragons was heavily influenced by MMORPGs. Such was the first thing I noticed about the new edition myself. It doesn't take more than a quick scan of the rules for someone who's familiar with both MMORPGs and older editions of D&D to see where much of the design changes came from. At first I felt rather leery about he changes myself, but actual play sessions reassured me that if I was going to play D&D anyway (it's far from my favorite RPG), I wanted it to be 4E.
Having spent my childhood immersed in the earliest RPGs; watched the appearance and evolution of home computers; and witnessed first hand the vast influence D&D had in shaping online RPGs; I find it rather poetic to watch the feedback loop complete its cycle, and see the online RPGs take their turn at re-shaping D&D. It does make for a very different game indeed, but different isn't always bad, and we learned a lot of valuable lessons about game design online. There's a few design choices in 4E I'd happily take issue with, but all in all, the things people gripe about the most were just as bad -- if not worse -- with older editions of the game when they first came out. Give it some time for the D&D community to soften the hard edges of the new version, and there won't be a heckuva lot left to recommend the older versions to anyone but their most rabid devotees. As far as I'm concerned, what MMORPG games bring to tabletop rules is far less problematic than what the MMORPG players themselves are bringing.
You can get problems in both directions, of course. Over the years, I've witnessed countless ill-conceived attempts by tabletop role-players to plug their expectations into an MMORPG setting, only to see all their best laid plans go up in flames because the social dynamic on an MMORPG is nothing like the one that goes on at the gaming table. For a tabletop game, you can take a proclomation like, "All dwarves would rather die than live in dishonor," and run with it as a universal truth in your campaign, because it's possible for five or six people to come to some sort of concensus on what dwarves would consider honorable. Pack a thousand different players of dwarves into one game, though -- half of them having only picked the race in an effort to max out their key combat stats -- and that one simple statement becomes a powderkeg as players abandon all sense of civility in the war to decide who gets to define dwarven honor. I know of such a feud on one MUD (aka: text-based MMORPG) that had been dragging on for about seven years last I checked, ruining the fun of countless players and admins alike.
Now it seems the shoe is on the other foot as more and more MMORPG players are getting lured into the ranks of the tabletop role-players by friends who play both ttypes of RPGs and by tabletop products marketed at the MMORPG demographic. Like all those tabletop gamers who came to the MMORPGs thinking they already knew the terrain, MMORPG players are showing up at the gaming table with their own potentially toxic preconceptions. Perhaps the worst of these is the drive to squeeze every last ounce of efficiency out of their characters' stats.
Power players have been with role-playing games for as long as the hobby has exsted, but MMORPGs take the allure of power-play to a whole new level. With direct GM intervention at a minimum, the experience is necessarily mechanics driven rather than story driven. Sure, it’s possible for MMORPG players to agree to conduct storylines among themselves, but the ability to make a real impact on the environment always starts — and almost always ends — with a player’s ability to game the system. To make matters worse, the repetitive grind of accumulating wealth/power by doing the same activities over and over (the faster the better) magnifies the effect of every tiny little advantage that players can eke out for themselves. e.g.: A +5% to-hit in a table-top game (where it should give no one pause if you swing your sword exactly ten times all evening) is nice, but that’s only a 50/50 chance it’ll change the outcome of even one die roll that night. In an MMORPG, on the other hand, where you might swing your sword twenty times in a minute, you could land 100 extra blows with that +5% before the tabletop players agree on where to order pizza.
Another concept that MMORPG players take to new heights is that of "game balance". That D&D 4E strives so hard to balance every class against every other class, every race against every other race, is one of its most MMORPG like aspects. In MMORPGs, it’s a huge deal for factions to argue back and forth, forth and back about game balance (which they invariably define as, “no one else can best us in combat — at least not with any frequency”). First one side cries foul; then the other side taunts it as a bunch of cry-babies; then the admins tweak the programming; then the side that had an advantage screams, “We’ve been nerfed! I don’t know why we even play this stupid game!”; then the balance of power shifts and another faction starts screaming bloody murder about the unfairness of life and of no-good, weasely game admins.
The thing that so many of these new players fail to understand is that as soon as you’re sitting down face-to-face with a game master, the whole nature of the activity changes. The GM can kill their 523rd-level, 65-strength warrior demigod as effortlessly as he can kill a 1st-level peasant farmer. There just aren’t any Joneses to keep up with anymore, so a player might as well ease up and enjoy the unfolding, highly personalized story and the company of his friends — because if all he wants is to prove his imaginary-martial-prowess, there are much, much better battlefields to prove it on these days.
Having spent my childhood immersed in the earliest RPGs; watched the appearance and evolution of home computers; and witnessed first hand the vast influence D&D had in shaping online RPGs; I find it rather poetic to watch the feedback loop complete its cycle, and see the online RPGs take their turn at re-shaping D&D. It does make for a very different game indeed, but different isn't always bad, and we learned a lot of valuable lessons about game design online. There's a few design choices in 4E I'd happily take issue with, but all in all, the things people gripe about the most were just as bad -- if not worse -- with older editions of the game when they first came out. Give it some time for the D&D community to soften the hard edges of the new version, and there won't be a heckuva lot left to recommend the older versions to anyone but their most rabid devotees. As far as I'm concerned, what MMORPG games bring to tabletop rules is far less problematic than what the MMORPG players themselves are bringing.
You can get problems in both directions, of course. Over the years, I've witnessed countless ill-conceived attempts by tabletop role-players to plug their expectations into an MMORPG setting, only to see all their best laid plans go up in flames because the social dynamic on an MMORPG is nothing like the one that goes on at the gaming table. For a tabletop game, you can take a proclomation like, "All dwarves would rather die than live in dishonor," and run with it as a universal truth in your campaign, because it's possible for five or six people to come to some sort of concensus on what dwarves would consider honorable. Pack a thousand different players of dwarves into one game, though -- half of them having only picked the race in an effort to max out their key combat stats -- and that one simple statement becomes a powderkeg as players abandon all sense of civility in the war to decide who gets to define dwarven honor. I know of such a feud on one MUD (aka: text-based MMORPG) that had been dragging on for about seven years last I checked, ruining the fun of countless players and admins alike.
Now it seems the shoe is on the other foot as more and more MMORPG players are getting lured into the ranks of the tabletop role-players by friends who play both ttypes of RPGs and by tabletop products marketed at the MMORPG demographic. Like all those tabletop gamers who came to the MMORPGs thinking they already knew the terrain, MMORPG players are showing up at the gaming table with their own potentially toxic preconceptions. Perhaps the worst of these is the drive to squeeze every last ounce of efficiency out of their characters' stats.
Power players have been with role-playing games for as long as the hobby has exsted, but MMORPGs take the allure of power-play to a whole new level. With direct GM intervention at a minimum, the experience is necessarily mechanics driven rather than story driven. Sure, it’s possible for MMORPG players to agree to conduct storylines among themselves, but the ability to make a real impact on the environment always starts — and almost always ends — with a player’s ability to game the system. To make matters worse, the repetitive grind of accumulating wealth/power by doing the same activities over and over (the faster the better) magnifies the effect of every tiny little advantage that players can eke out for themselves. e.g.: A +5% to-hit in a table-top game (where it should give no one pause if you swing your sword exactly ten times all evening) is nice, but that’s only a 50/50 chance it’ll change the outcome of even one die roll that night. In an MMORPG, on the other hand, where you might swing your sword twenty times in a minute, you could land 100 extra blows with that +5% before the tabletop players agree on where to order pizza.
Another concept that MMORPG players take to new heights is that of "game balance". That D&D 4E strives so hard to balance every class against every other class, every race against every other race, is one of its most MMORPG like aspects. In MMORPGs, it’s a huge deal for factions to argue back and forth, forth and back about game balance (which they invariably define as, “no one else can best us in combat — at least not with any frequency”). First one side cries foul; then the other side taunts it as a bunch of cry-babies; then the admins tweak the programming; then the side that had an advantage screams, “We’ve been nerfed! I don’t know why we even play this stupid game!”; then the balance of power shifts and another faction starts screaming bloody murder about the unfairness of life and of no-good, weasely game admins.
The thing that so many of these new players fail to understand is that as soon as you’re sitting down face-to-face with a game master, the whole nature of the activity changes. The GM can kill their 523rd-level, 65-strength warrior demigod as effortlessly as he can kill a 1st-level peasant farmer. There just aren’t any Joneses to keep up with anymore, so a player might as well ease up and enjoy the unfolding, highly personalized story and the company of his friends — because if all he wants is to prove his imaginary-martial-prowess, there are much, much better battlefields to prove it on these days.

Re: your last paragraph
Re: your last paragraph
A game master can achieve absolutely anything within the game setting. Whatever he chooses to make happen will happen. His personal agenda for his world must and will win out, and the only leverage the players have comes from being part of that agenda . Even once the game rules have been decided, the GM's biases get infused into the planning of every encounter; the execution of every ad-libbed event; the choice of every random generator to use or discard; the interpretation of every single rule and die roll… So if you don't like your GM's personal agenda, you're never going to like his game.
There is no one simple answer as to why, despite this, 4E strives so very hard to achieve balance in combat prowess between all types of player characters. Rather, a number of converging factors come into play at once. Marketing, accessibility, and inter-player jealousies all have a lot to do with it.
WOTC wasn't founded as a game publisher so much as it was founded as a marketing plan. No gamer who was around at the time can forget the way Magic the Gathering broke over the community like a tidal wave of crack cocaine. To this day, I refuse to play collectible card games, not because I have any doubt of their quality, but because they're built on a business model that strives to create a culture of addiction. I seriously doubt WOTC ever releases a product line without a long-term marketing strategy in place, and part of 4E's marketing strategy is tapping into the huge mass of MMORPG enthusiasts who have never played a tabletop RPG before. 4E was built from the ground up to appeal to their (aggregate) sensibilities, and those sensibilities include a rabid interest in combat balance between player characters.
The accessibility factor here also ties directly into the marketing factor, in that D&D is the "gateway drug" of role-playing games. It was the first; it remains the most recognizable brand name; and having grown directly out of more traditional game formats, it retains a lot of vestigal qualities of traditional board games that new players find familiar and comforting. One of these qualities is the focus on "winning", which in D&D is accomplished by racking up experience and gold pieces like points in a pinball game. RPGs which strive to take the focus off of winning (the destination) and put it on storytelling (the trip) still have their methods of rewarding players, but the rewards don't get tallied up encounter by encounter with the same sort of "you did X, so now you're entitled to Y + 7 times the square root of pi" algorithms that have always been a trademark of D&D.
(continued in next response…)
Re: your last paragraph
From the game's earliest days, when it established "referee" as a synonym for "Dungeon Master", D&D has fought to maintain the conceit that the game master is a neutral, unbiased arbiter of the events that simply flow around him. But the inevitability (and importance) of GM bias and personal agendas are the elephant in the room that D&D tries to ignore, precisely because it's uncomfortable to those players who are focused on winning the game. Everyone likes to have bragging right (whether they use those rights or not), and a lot of players like to think that defeating the Demon Lord of Ultra-Cool-Badness at the D&D table equates to winning the homecoming football game. It doesn't. Maybe your DM demands that you be both resourceful and lucky, maybe he doesn't, but odds are that no matter how much hell he puts you through, he's secretly rooting for you to win in the end. If that's true, at some point he pulls his punches without even thinking about it. If not, he's stacking the deck against you in the same way. No matter how you try to dress it up, tabletop role-playing is seldom about peer-vs.-peer battles, and never about a raw, unforgiving struggle against some make-believe universe. It's improv storytelling with some complicated ground rules.
As to the inter-player jealousy factor, every single PC is the hero of his own story, not someone's sidekick. A truly balanced tabletop RPG is one that gives every PC an equal chance to shine at his own specialty. Since D&D is at its heart a dungeon-crawl combat engine, balancing the game means giving every PC an equal chance to shine in dungeon-crawl combat. Other games can afford to stress less about combat balance because they provide a broader spectrum of opportunities for PCs to show off their special gifts, but D&D cannot.