Seriously, the exposed midriff is a purely decorative costume element, like the high heel. It serves no functional purpose; in fact it's impractical in combat situations. It's only all the more obvious when the females are placed beside their more sensibly-clad male colleagues. So why so many midriffs among superheroines? Because it's fashionable in the real world? Because it's sexy? We're not saying that midriffs are inherently bad. But midriffs DO indicate the inherent difference in the way female and male superheroes are treated- even in so-called "wholesome" children's TV shows. What do midriffs say about the character?
The next time you design a superheroine with a naked belly, first ask yourself why.