a)How come they did away with net cord people to pick up lets?
b)How come quite often you hear an audible noise as the ball goes over the net that could only really be the sound of the ball clipping the net and yet nothing is called?
The system they use currently is more accurate. The sensor picks up vibrations of the net, and makes a beep whenever there are too many vibrations.
Although, this is not 100% accurate. At times, the ball passes just over the net and the sensor still beeps.