All these rules are there for a reason. I completely agree with you that it is perfectly all right to leave electronics on when you are giving rides. Even in the very unlikely chance that a device that your friend has is faulty, and by some wild chance it self-excited at an entirely wrong frequency and started transmitting wildly at CTAF, so what... It is a perfect day, and you'll land no problem.

But airline pilots are routinely flying IMC. They do want their radio aids working. And there is just no knowing what faulty device of some shady manufacturing one of these five hundred passengers is using. Who knows. May as well " interfere with the navigation systems" at a wrong moment.