It's possible your motherboard has both 1.1 and 2.0 USB ports, although not many boards were made this way, as far as I know. I have an ECS K7S5A Pro motherboard that originally had USB 2.0 on back but the front ports were 1.1. I later added a PCI USB controller card that allowed me to convert to two front ports to USB 2.0 and added two addtional ports on back.
The fact that Device Manager shows only one instance of "USB 2.0 Enhanced Host Controller" does not mean that you only have one USB 2.0 port. If all your ports were 2.0, Device Manager would still only show "USB 2.0 Enhanced Host Controller" one time.