usb isnt a simple protocall its similar to half duplex cdma ethernet
even the pic 18 isnt designed to be a host just a device connected to a host .

i believe that in the near future most coputers will be shipped with
no serial or parallel ports just ethernet , usb 2 and maybe firewire
actually you can connected everything just using usb 2 and converters +hubs if you run out of connections
stuff a bluetooth into a usb .
apple had this plan years ago when perfected its a great concept
pbp only allows you at the present time i believe to talk to a pc using usb emulating a serial port .
its not really the sophistication level we need in our modern times