Wasn't Fez's late-game gameplay considered spoilers? It's not really related to the story at all, but nobody wanted to talk about THE REVEAL until weeks after the game was out, because everybody knew that was a really amazing, unexpected moment.
So I can see it being considered spoilers in some circumstances. The first time I played Metroid, for example, I was always really excited to see what the next weapon/ability I would get was, and I would've been really pissed if I was reading Nintendo Power at the time and they revealed every single ability in the game to me.
I definitely think that there's an argument to be made here about gameplay being spoilers.