I don't think it needs to be made sense of…there has been some improvement in this area but there are still some goofy gender issues regarding portrayal, including costumes.
I don't need a costume to be practical, I think that's a dead end argument. If these characters really existed, I suspect some would be wearing costumes that made them FEEL confident and powerful, and for some, that's going to mean heels, or armor, or exposed skin, or a manga-esque look, or something.
But it has to fit the character in some way. It doesn't make sense for Kitty Pryde or Donna Troy to wear a thong and pasties. But I can definitely see Power Girl's boob window. It fits her established character.
Still, if we had guys dressed that way more often, it would take some of the sting out.