Actually, even a marginal power supply will provide the 500mA needed for USB ports, but the problem is that power will be distributed across all of the ports. The requirements of CH controllers, or any high powered USB device, can be cheated of available power if there are even a small number of devices plugged in. It is not that they will not work, but it is because when the power drops below a certain level the USB port will drop devices from identified to unknown, and then when they are recognized again the mappings may easily be confused (requiring you to remap the device in AH).
Overvoltage protection on a powered device is also much better than a strictly MB port setup. Although each generation of Windows has usually brought about better power management, I have still seen USB devices ruined by overvoltage (cost me a CH Throttle Quadrant just recently).