Various devices tend to either have serial number empty (for example both my keyboard and mouse, Sun and Logitech respectively, so not exactly cheap Chinese crap) or filled with some random garbage that is not unique at all ("123456", "Serial" and so on).

One would assume that "garbage in iSerial" is workaround for Windows' behavior of identifying devices by either it's serial or physical port and requiring distinct driver registrations for devices that are "different" according to this logic.