This conversation just made me realize that maybe the reason why I've been following Supernatural (well, obviously I've become avid because of Castiel alone) and finally been hooked to actually care outside of the bubble that is Castiel's World... is because so much of the current apocalypse arc had been ripped off Neil Gaiman's books.
Of course my kneejerk reaction as a Gaiman fan is a wtf.
Crowley being Crowley... when a black car wheeled in, I actually expected to see the Bentley. Admittedly, I kept looking for the Bentley throughout that episode.
Anyway, back to the point. There's nothing new under the sun. It's only a matter of being able to pull something different from an existing idea, which is what SPN has done thus far (hello Cas~~~ keep existing). Crowley was just the biggest most obvious ripoff that it makes me wonder if Kripke at least talked to Gaiman or if they're buddy-buddies enough that borrowing Crowley is just that, 'borrowing' or even 'homage' to Neil Gaiman's epicness.
Taking off from Gaiman's (and Pratchett too but I'm not as well read into Prachett books so I wouldn't know if SPN took a lot too) stories as the SPN modus operandi would certainly explain a few things.