Pawsplay - I believe that we're coming at this from opposite ends.
For you, you look at the prohibition to commit suicide for the PC and say that that prohibition makes the game no longer an RPG. I look at it as, this is an act that is totally out of character for a character in this game, and as such will almost never come up in play, thus it's effectively the same as flat out ruling you can't do it.
An option that no one exercises is no different than no option at all, IMO.
From what you are saying, if I add a rule to D&D that says you may not have your PC fall on his own sword, that makes D&D no longer an RPG. I disagree, obviously. I think that the odds are fantastically small that you will ever fall on your own sword in D&D (at least deliberately, without adding in critical fumble tables

). As such, I have no problem saying, "You cannot commit suicide with your character" and still have an RPG.
I believe that should clear up Ariosto's apparent lack of reading comprehension abilities as well.
As far as role assumption, I think you are conflating role with class or profession. Fighter is no more a role than accountant. That's not who you are, it's just what you do. What differentiates two D&D fighters with identical stats and equipment?
To me, the difference is the roles that the players assume for those characters. One might be a noble knight and the other a gutter brawler. One might adhere to a code of conduct, the other swears fealty to a liege. On and on. The role that you assume with these two characters has little or nothing to do with class.
That brings us back to Monopoly. You do not assume any role in Monopoly. The game certainly does not expect you to. You play as yourself all the time. The fictional job of hotel builder is there, but, it in no way has any impact on how you play the game. There's no more role in Monopoly than Chess. I'm certainly not expected to act like Sun Tsu or Kasperov when I play chess. I might immitate some of their tactics, but, that's about it.
I'm certainly not expected to act like Donald Trump when I play Monopoly either.
Now, I can, but, the game does not place this expectation on me at all. I can be entirely myself, making decisions without any guidance from the role I have assumed. There is no more role assumption in Monopoly than in Snakes and Ladders.