That's why I'm suggesting they don't really care if a few passengers are violating the rules. The reality is they HAVE to know that some people are going to intentionally violate the policy...and even more will accidentally leave a device on for the duration of the flight. My assumption is that the measurable interference caused by this small number of devices is so low as to have no (measurable) effect on the electronics in the plane...but that they are simply erring on the side of caution by restricting them. If this was not the case the flight crew would no doubt be much more vigilant in their effort to prevent their use. I mean if you were a flight attendant and actually felt the plane was in danger wouldn't you?