USB can be "Hot-Plugged" unlike Parallel or Serial Port devices.
I know of some printers that are NOT faster using USB !
One that stands out is the Hewlett Packard 895cxi
It runs on USB or Parallel
Oddly, parallel print speeds were Faster than on USB, the testers were baffeled too.
Some items conflict when multiple USB devices are used.
This particular Printer pitches a fit when used in combination with a USB scanner, it takes about 5 minutes to print a plain text sheet.
This is obviously very wrong.
When set up correctly, this Professional printer prints a text page in 3 sec or so. A 8x10 Glossy Photo on Best in about 5 minutes.
Agree that USB is limited, I'd hoped the USB'2 would be "backwards-compatable"