They only make you turn your music off during take off and landing. Which are the points during the flight where something is most likely to go wrong. If you are issuing emergency instructions to people you want to say it once and them get them either into the brace position or off the plane sharpish. What you don't want to have to do is keep repeating yourself millions of times so the clearing in the woods who can't cope without his trip-hop soundtrack can hear you.
Once you're in the air you've got more time and its safer.
Those instructions are given before takeoff. People at emergency exits are told what they need to do and if something is going wrong I think I'll take my headphones off.
Look Flying is by a ridiculous distance the safest way if travelling. I don't get all these special instructions when I get on a train despite it being more dangerous or a bus or the death trap that is a car.
There is no way my device is emitting anything at all bar heat and light and possibly some harmless radiation. It poses no threat to the aircraft and as such I should be allowed to listen to my music unmolested.
Please take this in the spirit it is intended but I can't work out if this is epic stupidity or breath-taking arrogance on your part.
DURING take off/landing ie. when the plane is in the air the flight crew are seated as well so no, I agree, they are not giving safety instructions. The only exception to this is during an emergency landing/crash where the crew will give out additional instructions BRACE BRACE being one example that it might be in your interests to hear. If you are plugged into your mp3 player or whatever you won't hear it and consequently will probably not only endanger yourself but others as well. Its not a challenging concept to grasp is it?