I still believe the issue is more deeply rooted in passenger safety than in actual electrical interference. Take-off and landing are generally regarded as the most risk-prone activities for an aircraft. Having passengers at least slightly less disengaged likely benefits everyone. Not to mention it is arguably unpleasant to have 200 tablets flying about.
"Sir, please shut off your electronics device as it may interfere with the navigational systems."
"Um, no. Did you SEE that episode of myth busters?"
"Oh. Well.. um.. the real reason is so you pay attention".
You can't just change the reason because your original reason has been proven wrong. If this was the real reason, then they should have been upfront about it.
But like a sibling commenter states - reading a book (as opposed to a kindle), or being deaf (as opposed to wearing earphones - this one's probably a bad comparison..) carry the same 'risks' and neither are banned.
My counterpoint to that would be that I can still sit and read a hard cover copy of Godel, Escher, Bach. It'd keep me just as disengaged and is certainly more dangerous than an iPad when airborne.
