As we know from comic books, Superman's birthplace was Krypton (which would lead us to assume he is not from the USA) -- but the following would suggest he *is* indeed American and not an alien as we'd assumed.
http://en.wikipedia.org/wiki/Krypton%2c_Kentucky

... and we had always assumed Batman was American... well, perhaps not...
http://en.wikipedia.org/wiki/Batman%2c_Turkey