Superman isn't exclusive to America. Superman is meant as a worldly figure. Aside from being Kryptonian, Clark may have been raised in America, but he does not represent just America. Therefore you can get away with that. That whole "Truth, Justice, and the American Way" is just a product of the Donner era.
Bond is exclusive to England. I get acting, but there is authenticity which would be nice to maintain. Bond is English to the bones. I don't mind Sherlock Holmes being played by RDJ, but it's always nice for some things to stay authentic, as Holmes could have been. It's like Harry Potter and some of the cast being American. For authenticity sake, they should keep it. Because God knows a lot of stuff becomes Americanized anyway. I'm not one for "TRADITION!!!" but there has been a nice streak of consistent English actors. I would like to keep it that way. I'm not even English and I would like to see Bond remain in England. Why fake it when you can have the real thing that's always been there? Especially since they've come this far with consistency.