Is the USB hub in the display supposed to show up in System Profiler like the hub in a keyboard? That might shed some light.

Also - could you test these ports for if they are getting 5 Volts like they should? One way to test this is by plugging some sort of device that charges off of a USB port and seeing if it starts charging. If you're just missing the 5 Volts, that probably wouldn't be too terribly hard to fix.