JMS has said of the costume that form follows function. Which seems a fair comment.
But why does Batman wear a cape?
Think about it. The guy stalks around the urban landscape like a ninja. How does that thing [and it is pretty huge depending on who draws it] not get snagged on rootop antennae, fire-escape ladders, gargoyles...?
How do you fight in it. Beating up street thugs is probably not that challenging anyway, but what about Killer Croc? Or Bane? I think you would have a lot easier time using martial arts techniques in a "Ms America bathing suit" than a Count Dracula costume.
And speaking of martial arts, dont its practioners usually dress in loose fitting clotes to give them greater freedom of movement. Skin tight pants would seem like the opposite of that. I guess Trinity in the Matrix got it wrong - which is kind of the point.
That's the thing with super-heroes. Once you start picking stuff apart for practicality or realism the whole genre just unravels. I mean, is it in any way realistic to think that Peter Parker just invented those web-shooters and the the formulae for his webbing out in the garage? That webbing concoction alone would probably win him a nobel prize.
I liked Gloria Steinhams point that the ancient Greeks fought in skirts. I dont remember anyone sitting in 300 watching the Spartans unleashing hell commenting that they looked like panzies.
The costume change is there, fine. But just tell us it was to get media attention and booste sales. Don't make up explanations about practicality or realism while Batman performs olympic gold medal acrobatics with a kite sail on his back.