ExploderWizard
Hero
Perusing some of these responses, I tihnk the OP has received a definite answer. A roleplaying game, at least a traditional roleplaying game, needs to have a coherent world and inhabitants or the game is unplayable. The game, again for traditional RPGs, has been about creating and enacting strategies and tactics within a fictional world. The degree to which the game world is or isn't predictable is the degree to which the players can or cannot strategize within it. No plans or preparations can really be made in relation to an incoherent (or worse, inexistent) world. This is why we have adventure modules. And campaign worlds. And book after book of detailed characters and items and places and more. It is to define an understandable world for the players to discover.
I'm not going to get into the specifics defining between realism, verisimilitude, and fantasy realities. But a game world that cannot be understood by its' players definitively cannot be successfully roleplayed within.
I agree with this assessment. Expanding upon this premise of a world with a defined reality (no matter how realistic or unrealistic it may be) the players need to be informed about what is obviously perceptible about that reality. This doesn't mean that thier characters have to know how everything in the world works. There are a lot of people in our own world who don't understand the math behind basic physics but they can recognize "normal" behavior based on these physical principles when they see it.
Such basic understanding of baseline world knowledge is essential in order for the strange and mysterious to have any real meaning. I enjoy using different basic physical and magical laws for other planes of existance. These differences are only meaningful if the prime material plane is consistent in this regard.
Baseline realities don't have to be the same as those of the real world. A fantasy world could feature slightly less gravity than earth which would mean that heroic jumps, and leaps would be accepted as normal in such a world. The important thing would be that characters from this world know through common knowledge that such feats were "normal" and wouldn't have the same "Wow!!" factor that they would on a world with normal gravity.
I prefer using the realities of the real world with well defined exceptions. The trick to maintaining consistency isn't in sticking to reality its in ensuring that the players are not suprised by something that thier characters would know by default.