I must be getting too old to cover this stuff, because for some reason that bugs me. I can see the X-Men and Spiderman movies being rated PG-13, but for some reason in my head I always pictured Superman as a PG character. In the comic books X-Men and Spiderman have always seemed more suited to a PG-13 rating, the former dealing with issues of prejudice and alienation and the latter dealing with teenage angst and the realities of daily life and trying to squeeze in being a superhero when you can't afford to pay rent.
But Superman... Superman is a product of an earlier, more innocent age. In addition to that he was raised by good parents on a good ol' farm in the Midwest and he has morals and virtues that make Captain America look pale by comparison.
I guess that's part of the reason the Superman titles languished for a while. He became kind of an anachronism, out of touch with the times and with what was going on in other "edgier" titles.
I don't normally read Superman comics, but I've picked up a few issues here and there and from what I've seen DC has worked hard to try to bring him into the world of 21st century comic books, concentrating more on his humanity and the issues he faces day to day. Of course they had the whole "Death of Superman" thing with the villain Doomsday a while back, and that storyline would certainly warrant at least a PG-13 on the big screen.
I guess in the end I'm a bit ambivalent about this film. I suppose that considering how all the promotional material I've seen so far (trailer, photos, upcoming movie-related statues) have left me with zero excitement factor for this film, the PG-13 rating is probably a good sign that there will be some cool battle/action sequences in the film.