I get it there is a minute risk that electronic devices may interfere with aircraft systems - but I've always thought perhaps more importantly that it was that during these critical periods of flight (take-off, approach, landing and to a lesser extent taxi), that it's safer from a crew/passenger standpoint if no one is distracted watching personal video / listening to music in case an emergency arose and crew needed passenger attention.

On the digital camera issue - it's been 2 perhaps 3 years that only a few have had wifi capabilities - I can't believe this rule which way predates the onset of wifi in cameras was actually intended for those that want to take a snap out their window.

When is takeoff over? As soon as crew are buckled in and out of eyesight of one reinserting earbuds . Just kidding...