This is something that I've noticed, and I pointed it out in another thread earlier.
Traditionally (read as: In the comic books), Spider-Man isn't a character that represents "good in America" (nor does he has a "red, white and blue' costume, it's red and blue, the white's only in the eyes, and they don't really count, but whatever), Superman does. Spider-Man was intended to be the 'dark horse' of superheroes, where he's different from the "classic" definition of superheroes, but in the movies, he's the ONLY one who actually lives up to that standard. The placement of the flags in Spider-Man, and the "Truth, Justice, all that stuff" in Superman Returns shows that (in this case at least) the roles have been reversed, and Spider-Man is beloved by the public, where as Superman is no longer a symbol of the "American way".
The truly sad part is, while both changes are interesting and thought-provoking on paper, only Spider-Man's new-found adoration works, where as a depressed, moody toned Superman seemed to turn off a lot of viewers.