My guess about #4 is that it is a holdover from the days of tape player and analog cell phones. These devices were high-powered (meaning more interference) compared to mp3 players and digital cell phones.
I would also note (RE: #4) that the map and the ads during takeoff and landing don’t have audio — so you will hear the announcements that the plane is going down!!!
The wikipedia phrase ‘citations needed’ would fit the bill for most questions about public policy. But then again, where would the public be if everything was rational, explained and transparent? Here in NY they want to make a law so that anyone using instruments to monitor the environment must get a police permit or else go to jail.
I have been studying in Cranfield University, UK where most of these rules were developed. I have not asked the same exact question, but the general idea is quite simple. So, to answer the questions: 1 and 4 are required so that passengers are aware of the process of take-off and landing and if something goes wrong would have the chance to react. Take-off and landing are the most dangerous parts of the flight and if something happens, there will be no time to make an announcement. Therefore crew drills the emergency position into your brain before each flight with a hope that at least some people will take that position instinctively if something goes wrong. Removing the distracting entertainment and ensuring that all people have the chance to look out of the window are easy ways to help that. Also during rescue it is helpful if the windows are open so one can look inside.
As for 2 and 3, the seats in the airplanes are designed to
absorb the shock of a crash by crumbling down. If you have your
seat reclined, it will break legs of the person behind you. Your
leg rests put your legs into a position more likely to break them.
If your legs are broken, you are unable to get out the plane on
your own and that increases you chances of dying tenfold (due to
smoke and fire). Oh and the table will break you neck 
Have fun, Aigarius
This one seems a good answer for the first one: http://answers.yahoo.com/question/index?qid=20061210024712AADdHtl
For 2 and 3: http://en.wikipedia.org/wiki/Brace_position might be relevant. As for 4, I guess crash safety instructions may be displayed in case of emergency, and then they won’t have a chance to be mistaken with a part of the movie.
Take-off and landing are, as is well know, the most critical phases of a flight. So, I’ll venture a guess here that besides the aforementioned brace position, it has to do with being able to evacuate a plane. Reclined seats and unfolded tables would clearly get in the way of people trying to get out of the non-aisle seats fast. Window shades being opened might have some aspect of maximizing lighting conditions if the electric system fails after a crash landing. These are just guesses though, IANAAE (I am not an aeronautics engineer).
On the fourth point, I honestly have no clue but to assume that
it has purely commercial reasons 
I have not understood yet why the cabin lights need to be dimmed during takeoff and landing … is it perhaps that in an emergency (ie a crash) it’s an advantage for passenger eyes to be sensitive to dark already? on another point, thanks for sharing the LCA slides; quite motivating although I think the “it will be ready when it’s ready” attitude re Lenny is a touch old-school. I’m just a user (migrant from Ubuntu); I think by now a release schedule could be published.
For point 4, it may be in response to Swissair Flight 111, which caught fire presumably due to faulty wiring in the entertainment system (which, apparently, according to another source, could not be isolated from its power source):
http://en.wikipedia.org/wiki/Swissair_Flight_111
While it may be more a “fix-the-feeling” type solution, it is true though that pilots are at their busiest on take of and landing, and have no time for trouble shooting. So, maybe they switch the entertainment system off at these times just to play it safe.
Another very contentious issue that is semi-related is the no electronics rule on landing or take off. See the (long) debate: http://groups.google.com/group/aus.aviation/browse_thread/thread/78c6bb82a13d3c8c/eb3d9a5f9c75ad85
which continues: http://groups.google.com/group/aus.aviation/browse_thread/thread/3f851794a6c91da1#9a475bf782f472e1
Brian May
