meh
I started turning my phone off as I didn't want to get some wild roaming charges as I fly along. I am sure at this time a cell phone or my kindle will not bring down an airplane. I think the regulation comes from the FCC as they are usually worried about interference for consumers. They worry about the consumers in the takeoff and landing path being bombarded with harmful interference, that is why you can turn your devices on at a certain altitude.
I suppose part of it may be that they don't want to chance having to remote control fly the plane with 20 iPhone hotspots blasting out the signal.