No, they do not move properly most of the time.
Lots of armors already have capes! The eastern ones, the Archon's armor, Byrnie, Brynja, and Courtly Outfit come to mind.
If animation/movement rustles your jimmies, why the hell did you get Mount and Blade: Warband in the first place?
And we all know how "awesome" they look. So would it really be worth it to strat remodelling/adding new items JUST for the capes? I think not.