isi, ideally yes. However some of the aircraft systems, particularly navaids, are very susceptible to interference, in fact necessarily so. The ADF for example has a very "open" frequency acceptance. Witness what happens to it if a thunderstorm is nearby.
Also, much of the problem is not with interference through the antennae and receiving equipment, but rather with a direct affect on the wiring, inducing possibly harmful frequencies in the wires.
If you've ever been in a car with the mobile phone near the stereo you will more than likely have experienced this. Even though the operating frequency of the car stereo is vastly different (two orders of magnitude in fact) to that of mobile phones, you still pick up the interference.
Granted aircraft systems are generally better protected against EMI, but it most definitely does still occur.
The level of risk is debatable ad nauseum, and until a proper study of any possible incompatibilities is completed I think the ban is correct.