Another reason that this happens is when the device's USB cable is ripped/torn/ has a small hole. I had gone to sync my iPad with iTunes and suddenly was getting this message. The only other thing I had plugged into my computer was my printer, so I disconnected the printer. Then I tried again, but still got the message.
I was stumped so I started looking at the USB cable itself, and sure enough, there was a tear in it, and it was quite small but it was a tear in the cable that protects the wires inside. That was enough for it to cause the problem, but to be sure, I used my extra USB cable and was able to sync no problem.
After syncing with the "good" usb cable, I tried to sync with the bad one, and sure enough I got the error message again.
Sometimes you don't always see rips or tears in those cables. Maybe it got pinched behind something or whatever, but the smallest in it is enough to do it.
So that is another reason why some might get that " because a usb device was drawing too much power from your computer, one or more of your USB devices have been disabled" messages.