Here's the rub... To the layman it is typically about the letter of the law. The reality is that laws and rules are open to interpretation. It is also about the intent and spirit of the law or rule, Etc. This is where it gets tricky. With the radio for instance, you are correct in that the FAR's do not specifically address who may use the radio. However the FAA, via court cases, have determined that if radio communication's are required, that is also a required act of operating the aircraft.