[Continued from below.]
2) Why are superhero movies so popular?
There are two strong reasons for this. First, the universe of comics is far smaller than that of books; thus even a second-tier comic-book character is recognized by more people than almost any novel's characters would be [Harry Potter aside]. For example, Daredevil is -- and was before the eponymous movie -- certainly more widely recognized than Captain Ahab. Films drawn from pre-existing fiction (which are not a new or even disreputable phenomenon) stand to gain more the more widely recognized their characters are; this practically explains the phenomenon in itself.
This effect is reinforced by the fact that comic books provided a generational link between the youth of the last generation and their own fathers. Now that those youth are today's fathers -- and, in this post-print age, their own children are not reading or collecting comics -- the silver-screen embodiment of an adolescent memory offers them a chance for a little of the same generational bonding.