[Tenex]

This question obviously revolves around your assumptions regarding the role of the GM. To me, the GM is not a god, he's more of a referee. The word of the referee (in any sport) is the end of the discussion. However, the ref must follow the rules of the game. It's not like a good ref just ignores rules he doesn't like.

I don't see that this limits the GM's creativity. It's like saying your character is going to be in a boxing match. The GM decides how loud the arena is, what color trunks the opposition wears, what tactics he uses, etc. But the GM can't say that the other boxer outweighs you by 35 pounds. If the GM can't make it interesting without resorting to making your opponent outweigh you by 2 weight classes then he lacks creativity.