Saying they "shriveled" or "shit the bed" is a bit of an exaggeration. As you're seeing in the finals, whenever GS starts to make a run, Toronto picks up the defensive intensity. The NBA officiating is allowing them to play a very physical game, and it really throws teams off their game when they are constantly being bumped and pushed - it's much harder to adjust to that some people think.
On a side note to that . . . it's interesting to read the in game / post game comments on the NBA finals. People like to point to a specific foul called as a sign of how "biased" the refs are. I will say that what the Refs DON'T call is more influential in the result of a game, versus what they do call. And the timing of those calls has a significant influence on the flow of the game.