Doesn't matter if they stick or not, the point is that dead never means dead and gone with this show, and it significantly lessens the impact of those deaths. I blame this partially on the rabid fanbase out there, who screeches and screams until the writers give in (whether a character is dead or alive). The difference is, bringing back live guest stars is a lot easier than bringing back dead ones. In fact, I think the only guest star people have been HOLLERING for, for years, who has yet to make a reappearance on the show, is Missouri. The list above is still a long list of people who should have been dead, but who were all brought back for another guest stint on the show. Most shows of Supernatural's nature will at some point bring back a late great fan favorite, but Supernatural really seems to just be going through the list.
I still love the crap out of this stupid show, but I'd love it a whole lot more if they hadn't set a precedent that caused my immediate reaction over Bobby's death to be, "Big deal, he'll probably guest star again later this season anyway."