Koster's grammar considered harmful

Some say Raph Koster is an idiot. I would say he's a qualified writer with a penchant for misappropriation of some words. For example, the words "fun" and "grammar" -- see Yehuda's review and StGabe's comments.
Because these two words are central to Koster's publications, A Theory of Fun and A Grammar of Gameplay, I fear that misunderstanding and misuse of these words will propagate throughout discussion of game design.