Superman has done what most other comic book characters have not/cannot: he has become part of the American myth. He belongs in the pantheon with Paul Bunyon and Pecos Bill (and even more currently relevant than these). He's god-like, but vulnerable, searching, and unsure of his place in the world.
We understand Batman, but with Superman, we dream. We might not be able to define what the "American Way" is anymore, but Superman is forever tied to it.