Huh. Maybe it was just that I fell in love with Dean somewhere in S2/S3 and started calling him baby instead of Sam, and that affected how I saw the whole show. Maybe it's: S1 is about Sam adjusting to the life of a hunter. S2 is about Sam and Dean dealing with John's death and then a shift to dealing with Sam's powers/destiny. S3 is about Dean finding out that he wants to live (you'll have to watch Kripke's mini commentary about "Dream a Little Dream" when I give your DVDs back to you). S4 so far (okay, so it's only 2 episodes) is about Dean's faith. My bunny of the moment (totally sparked by you saying that the writers are leaving Sam out on purpose) is this: Dean is still in hell. We already know that demons get off on Dean's emotional pain. So why leave him hooked and screaming with physical pain (or the metaphysical equivalent thereof) when they can manipulate his reality, give him back his life, get him to believe in God, and then tear it out from under him with Sam's betrayal (by working with Ruby and lying about it, and possibly more of an explicit betrayal) and the reveal that he's still in hell, God doesn't exist as far as the demons know, and no one's coming for him?

Huh. Interesting question about the host bodies. I never thought about the Colt and the knife taking their souls, just their mortal lives.