Before any of these devices were released, and before any of us knew
what they would do with the display when off, we had a few discussions about hoping they
would blank the screen when they're "off" so that Flight Attendants (for example) wouldn't insist that they must still be on.
Generally speaking, a blank screen is an evidence of "offness" that most everyone will accept. I expect that's why they've all mostly gone that route.
