I think you are totally right about the superhero and zombie-inflation. Should we not add vampires to that list as well?
The vampire fad comes back every generation or so. Now its Twilight and True Blood, back in the 90s it was Buffy and Anne Rice, in the 80s it was The Lost Boys, and so on and so on.
But, I have a feeling its about to crash. Twilight knock offs are overflowing at the moment.
Like I said in my Twilight rant, with a little luck the girls who grew up with Twilight will move on to GOOD literature.
I have a feeling The Avengers may be the film that kills the superhero film. Like Episode 1 and Land Of The Dead it has been so hyped up that I fear its doomed to fail.