some other crew orders can be disobeyed without penalty, at least in the U.S.
Errr, I don't think so. I think you'll find all crew orders have to be obeyed, its just that they don't have the time to stop every idiot who thinks only some orders need to be obeyed. I can drive my car over the speed limit, but it doesn't make it legal does it? Do you think "Well everbody esle does it" would be a good defence in court?
The rules in the UK are clear - cellphones are to be switched off. Not cellphones are to be switched off if you like, or unless you want to play a game, or if the man next to you has too many bags. If you're told to turn it off then do it and don't argue. That is the law. If you choose to flout the law and ignore the lawful instructions of the crew then you go to jail. Just like people do in the US.