I think the issue with the kindle is that it has text on the screen, even though it's off. No, or very little, electricity is coursing through the device, and therefore there is no real chance of it interfering with the airplane's electronics/telecommunications.
Yeah, try explaining that to a stewardess. Just turn it over, read the shitty airplane magazine and let the lady clear the plane. When she is in the back, seated for takeoff, turn it back over and keep reading. If she starts walking around again, turn it back over and go to the airplane magazine. If you have time during the middle of the flight, try to explain the workings of the kindle and the magic of eInk.
She probably won't follow you, as she is a stewardess.