Hope you don't mind me butting in. Your last point about Mary's friends...Mary recognised the demon didn't she? It hasn't been explained how or why. I thought that the reason her friends were killed was that one of them might know whatever she knew, and presumably that would be something harmful to YED. That was my take on it anyway.

PS. Great discussion topic. Very interesting. I'm afraid I go for the shallow option: JW - awesome dad becuase he produced Sam and Dean!