The real problem is the plane can be 30 years old
When you go on board a plane next time, look at the FAA certificate posted above the door. You will likely see you are flying in a machine that was built 20 or 30 years ago. It's a bunch of analog electronics flying in a digital age. And at tens of millions of dollars a pop, the airlines aren't about to fix their fleet anytime soon.
Landing and Takeoff are the most dangerous flight regimes, so it makes sense to have them off then. But realize that you can't ever really turn an iPad or iPhone off -- it's still on even when it tells you it's off (otherwise it would never see you press the button to turn it back on). For devices like these with no real switch between the battery and the brain, there's no reason to have to turn them off, just put them in airplane mode and put them in Sleep for takeoff and landing.
Finally, the reason you know that non-cell-phones are a non-issue is once an airline starts collecting revenue to rent you WiFi, it's amazing how fast the interference issue goes away for them.
