Much the same way two routers broadcasting different WiFi networks in the same space and received by two different computers don't really interfere with each other. It's all just EM stuff, you can apply standard EM communication protocols like modulation. However standards will still be necessary, it can indeed be messed with.
Haha. Not much, except clobbering each other. This is not too probable with two routers, but with a dozen, all trying to work at 2412 MHz ("channel 1"), the SNR tends towards 0.
