Superheroes are buff and overly muscular as part of a male power fantasy, not to be attractive to female readers. However, superheroines are only impossibly hot to appeal to the male sexual fantasy - not be part of women's power fantasies.
An article from Cracked.com about six historical badasses (4 of them being women) who made their achievements while living as the opposite sex. Being Cracked.com there is some swearing.