Most role-playing game systems tend to rely on the dungeon master for the story and to run the game and provide the scene. What about a role-playing game that is most player driven and the dungeon master is just there to make sure nothing goes all weird, any system like that??
I could say a couple of things about this by it might not be the answer you're looking for.
Anyway, I think it has to do with the players. Real role-players could just get some breadcrumbs and go with it for a long time without needing much intervention. The system doesn't really matter if you don't have players geared towards making it a great game because their imagination is blank.
The only other game I know that can do that with the label of 'RPG' is one of the games here, ROK II since actually promotes the player making their own story.