I see those as being pretty much the same thing, in that either way I'm making the decision the character would make even if it's not the decision I-as-player might want it to make.
The difference, as I see it, is that one is making decisions based on looking at my character from the outside and asking, "What would that person do?" and the other is making decisions from the imagined point of view of my character, i.e. looking out at the world from my character's eyes, as it were. I think both could reasonably be considered roleplaying in actor stance, with which immersion as a phenomenon is generally associated, but I think the former at least comes close to author stance roleplaying because the
player's priority of
doing what my character would do is taking precedence over perceptions that might arise from the organic inhabitation of the character, and then a motivation is being invented for the character to justify its actions based on what the player thinks it would do. I don't see how the resulting decision is any different from the one you, the player, wanted to make. Just because you, the player, might have had other priorities that you're ignoring in this case doesn't mean that this decision isn't being made based on one of your own priorities.
With one exception, I'd rather there be no reason to perceive a discrepancy in the first place. Play to what's on the sheet, more or less, and all is good.
The one exception is alignment. You can write whatever letters you want on your character sheet under 'alignment' but its your actions in play that'll determine what your alignment really is, should somebody or something detect for such.
I agree with you about alignment because I treat them as objective forces in the games I run. If I were to change a character's alignment, though, I'd inform the player, mostly because there are mechanical implications, in my games, in terms of reaction rolls for determining starting attitude and social interaction DC's. I would never change a character's ability scores based on the player's roleplaying, though, because I don't believe the two things can be in conflict.
Qualified yes. It's likely not a stated thing for a few reasons: one, to state it in writing would cause a tidal wave of arguments based on exactly how they wrote and defined what each number in each stat might represent; and two, because the designers probably feel like this using one's character sheet as a guide to role-play is so obvious a statement that it really doesn't need to be said.
It's funny. I asked if this was true in your personal game, and you answered as if you think it's true of the game in general. Consider the possibility that it's not stated as a rule because it isn't one.
It goes beyond simple intelligence, though. Charisma, persuasiveness, wisdom, bonds-traits-flaws, background - all of these things* inform one's roleplaying, and they're right there on the character sheet.
* - or, where such exist, equivalents in other non-D&D systems.
I assume we're talking about D&D because this thread is in the D&D forum. Of course these things on the character sheet
can inform roleplaying, but only inasmuch as the player chooses that they do. A player is incentivized, for example, to choose actions that rely on the character's strong abilities in case the success of the action is in doubt and is tested with a check. A player is also incentivized to play to their character's personality traits, ideal, bond, and flaw by the Inspiration mechanic. There's nothing in the rules, though, that says they must inform roleplaying. It's just not the way the system works.