I don't think fluff should be considered unnecessary. A teddy-bear without fluff is just an empty bag. In a game, the fluff fills out the world, giving it form. It's needed by both rules heavy and rules lite games. My term for rules lite games is usually "cinematic". In these game, the story and the narrative take precedence over number crunching or rules lawyering, just as movies often ignore what is "real" in favor of what is "cool".