Likewise, airlines have a "clean cockpit" policy disallowing small talk during landings. Do they monitor the CVRs and fine pilots who break this rule? I don't think so. Will some pilots find the rule exessive and make exceptions? Maybe. But the rule still has an effect, and is in place because of previous accidents where distracted pilots have been a contributing factor.
While I think this rule about electronic devices might be too stringent, and that it will eventually change, I don't think the airlines have overblown it. Pilots will handle instrument failures gracefully in 99.99% of all cases, and then there's the fatal accident where some stupid malfunction caused the pilot to screw up (AF447, and many others before). Because they know this is a "numbers game", they try to minimize potential problems, even though they may not be able to eliminate them altogether.