Your basic misconception is that its not recieving a signal. They all do. Then they compare the pulse width they have been sent to their current position. If its the same the servo doesn't move, if its different the servo moves.

The way it works is the transmitter sends out a string of pulses, with each channels stick position encoded in it from channel 1 to whatever. Its broken down in the reciever and sent to the individual servos where they update their position and starts over again at channel 1.