Actually, Nigel, the feedback is also off on the GWSs. At least the cheaper line. I think it's also the case for most servos. The reason why it doesn't matter is that in the intended application (RC vehicles) the user adjusts the pulse width via joy stick. Thus, the "pilot" compensates for the gross inaccuracy of the servos.
They aren't used much in tandem except for robot drive like the common sumobot. Calibration/compensation is pretty easy to do so robot builders accept the problem as a minor annoyance to have cheap, compact, easy to interface motors.