The USB cable is not included with the 'Factor because it is a totally standard, widely available part.
This cable is known in USB parlance as an A-B type, meaning it has one square-ish connector, and one flat one. The connectors should be standard size, not the mini type used by many cameras and mice.
It does not need to be specified for USB 2.0 – pretty much any cable will work. Anyone who has a computer will probably have a few.
