Confused Notions of What Constitutes Classic Literature

I am a big fan of the mash-up culture. I think that Larry Lessig is right on when it comes to the stifling affect of the current copyright regime. But, please, can we recognize that when someone calls one of the recent zombie mash-up books classic, they're not using the term literally. Shot in the Classic Literature section of the Simply Books bookstore at DFW:

They also had, of course, Pride and Prejudice and Zombies in the same section. Speaking of which, can anyone explain to me what's behind the absolutely viral obsession with zombies the past two years?