As far as I know, USB2 works like USB1 if you connect a USB1 device
to it. It has to do with the transfer rate. USB2 is faster than USB1.
But if the device is USB1, it is designed to run at the slower speed and
does not take advantage of the USB2 capabilities. Since USB2 is newer,
there are not many USB2 devices out there. USB2 will compete on
speed with Firewire transfer rates (allowing for things like USB2 external
harddrives, just like firewire external harddrives).