Why are superhero movies even PG as a norm? shouldnt they be G? they are based on comics which conform to the moralist comics code, ie the source material is G rated (dark knight is part of a more recent era of comics which is no longer bound by the old code. its an exception).
To add some perspective, what would you think about a remake of the Wizard of Oz with an R rating for nudity and profanity. How about Tom Sawyer and Huckfinn adapted to the big screen with that R rating, and the screenplay altered to be more commercially viable-- Jim is now secretly working for the 'railroad' and huck and tom have repressed feelings for each other.
How about King Lear being performed for over a 150 years with an alternate 'Happy' ending written by Johnson?
I'm not saying no to non-G super hero movies, just think about why PG-13 or R would be considered the norm, when the source material is so 'clean'