Let us use "Airplane Mode" During Takeoff and Landing

I imagine it's about not only the device's signal transmissions, but its physical weight.

Planes during takeoff and landing are at sharp angles with extra G-forces. If your iPhone was in your hand during this time and you accidentally let go, maybe the phone would fly at someone else with enough force to hurt them.

I guess it also has to do with getting the 'full' attention of passengers, during the most 'critical' phase of a flight.

(Shhh. I never power off. I use airplane mode all the time. Don't tell anyone.)

Wouldn't that be difficult and time consuming to verify?