Actually the Pegasos is USB 2.0 Full Speed compliant
http://www.usb.org/faq/ans2#q1But it's much less confusing to say USB 1.1.
Yes, there is a good reason not to use High Speed USB 2.0 - back when the original Pegasos was designed and prototyped it didn't exist.
The newer chipsets with the support don't support the older processor interfaces that PowerPC has, instead choosing to utilise HyperTransport and Intel's own technology NetBurst.
These are very x86 specific technologies, although you can buy "tunnels" which bridge the gap between one chipset and another, it's an expensive proposition just for a USB port or two.
A lot of PC motherboards still ship with older USB ports. A lot of them say "USB 2.0" when they don't support the 480Mbit speed rating.
At least we're being honest in this regard
