A GPS doesn't just transmit less, it doesn't transmit at all.

However the reason that you turn off receivers as well as transmitters is receivers down convert the signals they receive by mixing with another signal. So to create that other signal you need an oscillator and that can transmit a small signal. Put an AM radio next to your computer and listen to the interference for a simple example.

Just so you don't think I'm crazy (well I may still be but at least I'm technically correct here)

http://en.wikipedia.org/wiki/Intermediate_frequency

You mix your received frequency with your local to bring the received down to where you can process it. All oscillators transmit a small amount unintentionally.