The USB power might be the culprit, or may as well be a design flaw. My VT model expresses the same issues with the draining battery. Unplugging it doesn't turn off the power to the ports, which is why my controller has its lights on even if its completely off and unplugged. This isn't on its powered port either. I've not investigated the BIOS, but I will shortly to experiment with its power settings.
EDIT:Well, one can assume that Asus hasn't bothered to add a setting for USB power settings in their BIOS. It's always on, and not even their own utility lets you turn that off other than changing thresholds...