So logically either: There is a danger from these devices but 1, nobody has ever switched on an iPad/phone/ebook reader/tamogochi/iPod on a flight in the US - ever. Or 2, planes crash all the time but the government keeps it secret.

Alternatively an ebook reader doesn't emit enough RF to crash a 737.

On a recent Alaskan airlines flight you were allowed to use the $5 in flight WiFi - but Bluetooth devices were banned. That's some pretty specific interference!