You've seen my analysis of the first scene based on his fears, correct? So, based on the fact that Calamity tried to give David "Thematically appropriate" power that was solely based on his fear, I'm guessing it isn't always this way. I'm betting Calamity works a lot like the Nightwatcher, where she grants wishes she wants to and changes the ones she doesn't. The only difference is the bane is always tied to fear.