sorcs and warlocks are maybe uncommon classes? maybe that is why they are more powerful than the others, there is suppose to be less of them around?
It looks so far like sorcerous origins (why can't they be called bloodlines?)
I had just assumed at first that the level 3 power used a favor. If not, it would mean the warlock can never be sneak attacked, so I'm guessing it DOES take a favor.