They're in our movies. Every few years there's a rush of superhero films (and apparently a big rush as of this writing).
They're on television. We've been having superhero stories for quite a few years now. We've also had "superheroesque" shows like Buffy and Supernatural, which are superhero stories with other trappings.
They're in games, despite the fact that superhero games have a dismal history with a few shining gems.
They are, of course, in comics. Comics may expand their themes in North America, but it keeps coming back to superheroes.
So, why superheroes? Why are they everywhere, and even when they fade, why do they come back?