Where Would Superheroes Be Without 9/11?

There's a meme going around lately, saying that the September 11 attacks gave rise to our current boom in superhero movies. And there's definitely some truth to it — superheroes gave us a nice escapist fantasy in the wake of a terrible tragedy, and allowed us to talk about some stuff we couldn't have addressed in straight-up narratives. But how much of the past decade's superhero-mania is due to a desire, after 9/11, to explore stories about people who have great power, after an event that made us feel powerless? And how much of it was just a special effects-driven boom that would have happened anyway?