pemerton said:But that is not to say that the world dictates it, only that the world permits it. And permission is a much weaker concept than dictation ]
The above is what I hold to as being the mark of good rpg gaming, consistency with previously agreed to norms. That doesn't rule out either DM worldbuilding within a session (players go off map), or even occassional player worldbuilding in session like some systems and GMs allow (4e D&D, character roles a successful streetwise check to find some info, player describes the previously undetailed contact he uses to get info). Consistent and permited, not dictated.
Let me see if I get your argument howandwhy. An rpg for you is:
1) a world is created by GM and player authority outside the actual game playing session and establishes certain logic/truths/laws/objects/etc
2) once you step into a game session, players should think and act as if they were their character -- "roleplay". This should be consistent with their prestated background, abilities, and the game world. If a player wants to introduce a truth/object/etc into the game world it should be done out of session
3) the GM is the narrator of the world, and describes interactions based on the agreed parameters in 1)
4) it is better/easier if the players' have no more knowledge of the rules/game world that their character would. This helps in playing the role and experiencing the world as the character would (pity the GM in many heavy rules based systems...)
A lot of posters' points seem to argue that even if the GM or players' are given some worldbuilding authority in session, if it is permitted and consitent with the world, it adds to the fun and should still be called a rpg.
That is my point of view as well. If most of the time you are in 2) mode, and sometimes for the sake of fun you collectively allow some 1) to happen during a session it is still an rpg to me. Maybe for that very moment, you are not "roleplaying". Hopefully, howandwhy, that is not your argument -- purely definitional?
Roleplaying does mean taking on a role, but roleplaying games involve more than roleplaying -- rpgs include worldbuilding, roleplaying, and narration.