Unfortunately, it is very difficult to PROVE that your consumer electronics will not interfere with the avionics. It is even more difficult to prove that the other 150 passengers' electronics will not do so, when they are all broadcasting different packets at different frequencies.
Obviously, for an organization in charge of this sort of thing (FAA), the only easy choice is to say, "Do not use wireless transceivers during the most critical points of flight." No, breaking this rule doesn't bring down the craft. But guess how many on-board cell phones the plane is rated for? Zero.