[silvarilon]

I'd argue that they (sometimes) do.
I'd argue that you are "roleplaying" as soon as you make decisions based on the character you're playing, rather than based on yourself.

As an example:
When I'm playing Quake or Doom, the game gives me no motivation to think "as my character does" - I go in a room, I shoot stuff. If I don't, it shoots me. The only decisions I make are tactical. I, the player, am making those decisions.

When I'm playing Baldurs Gate, the game gives me choices for my *character* to make. Do I sweet talk the thief, or threaten him? As a player, I might still approach those choices as tactical problems, choosing what I think will best achieve my goal - but I have the *option* to instead approach them as roleplaying choices. When I'm playing Zugg the orc, do I try to threaten them more often than when I'm playing Eldril the elf? Probably. If so, I'm roleplaying, even if only to a small extent.

A game like Mass Effects, by my definition, certainly has roleplaying aspects. Most of the game involves running around and shooting - no roleplaying there. I couldn't parlay, cowardly run from the battle, or take any option other than using my player skills to attempt to win the fight. But when I hit a cutscene, it often gives me options that allow me to decide "in character" - especially since these options rarely display any clues as to which would be tactically more advantageous. Do I send in the fleet to protect the council, or do I hold them in reserve to attack the enemy? A tactical choice, but both presented as equally valid options. Which is more important to my character? That's my roleplaying choice. And after I've made that choice, it goes back to a non-roleplaying FPS game.

Of course, I might choose not to take advantage of those options. I might choose whatever I, the player, feel like at the time with no consideration for playing a self-consistent character. Or I might make the choices based on "what would I do in that situation?" - in those cases, I'm really not roleplaying. I have the opportunity, but I choose not to take advantage of it. Zugg the orc might be just as likely to attempt flirting as Eldril the elf, the character and name might make no difference to me other than the avatar displayed on the screen. But that's alright. This whole thread is about what turns people away from RP, I can understand why someone playing a FPS like Mass Effects might not really care about whether they stay "in character" or not during the cutscenes.

I wouldn't consider "character building" (as in, skill selection) to be roleplaying. When I play Diablo, I choose a barbarian or sorceress. I get different skills. I end up with a different character each time. But when I'm playing the game, like with Doom, I'm still making the choices based on the player, not based on the character. I'm choosing the spells my sorceress will learn based on what I'll find most fun, or based on what I think will give the largest tactical advantage. There's nothing built into the game to encourage me to think "Maybe I won't take ice magic, because that makes you cold and impersonal, while my Sorceress is a typically friendly sort of person" - I might still decide that, but it would be the player imposing a story on the game, and not the game encouraging that behaviour.

Wow, I rambled a lot.
In summary: For me, roleplaying starts at the point where a player will vary their character's actions based on their perceived view of the personality of that character.
i.e. the point where they start using the character as a puppet to play out a role, rather than just as an extension of themselves.