Radio signals are also electro magnetic. They both transmit data (which is what the rule says).

When I read the rule, I assumed it allowed GPS too. Really, a GPS is just a very accurate timing device. The satellites are just guiding beacons like stars. Furthermore the next rule says that a GPS may even be required without says that it is an exception. Which suggests that they are not against the rules.

This is one rule that I object to because it outlaws a device that can be used for safety and promotional purposes. The rule should at least allow a GPS, EPIRB, and VHF radio so that you can be rescued in the case of an emergency. GPS's that log information for future playback can be very useful for coaching and showing people what happened at an event that they didn't attend (think about what they did with the America's Cup).

I don't think it saves much either. The RRS already outlaw outside assistance. So, no one is getting an advantage. A GPS or VHF radio are far from cost prohibitive. Plus, for a lot of $$, it is possible to make an electronic device that measures speed and position with inertial guidance technology that does not receive or transmit anything.