Gordon @ We Fly Spitfires talks about the conflict between the gaming side of MMORPG's and the role playing side (if any) of MMORPG's. Thinking more about my post on irreversible choices in Dragon Age, I think this arises because of the way motivation and consequences have to work in an online game.
Learning through failure
Take the ubiquitous "move out of the fire or die" mechanic in MMORPG boss fights. Assuming good faith on the part of the developer (intended and implemented the content to be beatable), the point of the fire is to teach the player a lesson. When a fire appears at the player's feet and they begin to take damage, they are expected to move. The player's death, in the event that they fail to move, is intended to teach them that lesson - indeed, the only point of having visible fire at all is so that the player can know how far they need to move to stop taking damage. The player has knowledge of the consequences of their actions, and this makes whether they live to receive the reward for victory something that is within their control.
From that perspective, missing out on some reward because you didn't say the right thing to the right NPC feels like capricious game design. Unless you have looked up the details on some out-of-game site in advance, you cannot know the consequences of your choices at the time you make them. Whether or not you receive the reward is out of your control. (Note that I can't say whether this happens at any point in Dragon Age - indeed, it seems like many conversations reach the same outcome regardless of which of the options the player chooses to say.)
The catch is that, for the role player, having bad things happen to the character (and/or having good things noticeably fail to happen) is its own reward. As long as it doesn't happen so frequently that it feels like the game is abusing you, this type of story conflict is precisely what the role player might be after.
The problem that online games have is that they expect players to play together. Imagine that your guild spent hours on the journey to level 80 and it turns out that your tank can't possibly tank the dragon, because only the Dwarves that he pissed off are able to craft armor that can resist the dragon's fire breath. The consequences of that roleplaying decision are affecting more than the one player who made the choice (or did not if they didn't read the spoilers).
In this setting, there are real limits to how much damage you can do to characters as a result of role playing decisions. As a result, role playing is limited to false choices (the conversation proceeds to the same outcome regardless of player actions) and cosmetic stuff (whether the guards salute you in town).
It will be very interesting to see how Bioware deals with this in SWTOR/KOTORO, if indeed it actually is massively multiplayer in the traditional sense of the word.