Console Batman: Arkham Asylum players may have gotten the game first, but they'll never be able to dress Batman up like Captain America.
One of the joys of PC gaming is the ability to screw with stuff, like Batman's costume skin in Arkham Asylum. Over at the official game forums they've got a fan-made skin collection going, complete with apps and instructions on how to implement them in your own game. If Arkham can have gargoyles on the inside, then I see no reason why Batman can't dress as Nightwing, or the Green Lantern, or yes — Captain America. I particularly like the Batman Of Zur En Arrh outfit, which mimics the bat-suit Batman wore when he went bat-shit insane.
Batman Arkham Asylum Modded Costume thread!! [Official Forums - Thanks Stancis!]