I don't think they should either. Can you imagine if movie theaters emitted a frequency that blocked phone calls while you were in the theater? Yes it would solve the problem, but I don't know of a single person who would be happy with it. People shouldn't be talking incessantly on the phone on airplanes because of common courtesy, not because they CAN'T.
Just imagine this scenario. What if while you were on a 22 hour flight, your grandfather took a bad fall down the stairs and ended up in the hospital. When you land at your destination, you find out that he has passed away. Your mother tried to call you while you were in the air, but you no idea what was going on since the airline blocked the call. Thanks to technology you could've had one last chance to talk to your father before he passed away, but now it's too late.
Yes, this is an exceptional case, but that's the point. There are always going to be instances where technology can make a real difference in our lives, and I think common sense needs to dictate when we do not make phone calls, not the airlines.
Yes it is true that just five years ago you could not have made such a phone call at all, but does it really seem fair to restrict the way were are using this technology now that we do have that capability?