Maybe they just hired Browett so they would have somebody crappy to fire when somebody important left the company, so they'd balance each other out. Or maybe Ron Johnson is having second thoughts about JC Penney (which would be good). It's hard for me to see Forstall's departure as positive, but it's hard to say what was going on behind the scenes. If he wasn't into what he was doing, or he was causing internal friction, it's probably just as well that he leaves.
Maybe he will start a new company making something innovative--if thermostats are his thing, I can see the competition in that industry really heating up.