From my experience CD players and Mp3 players start the same track over again if you hit back once, you have to hit back twice to go back a track. Again i don't really care either way, was just so use to having to hit back twice it messed me up a little bit until i figure out what was going on.
The TV apps do this type of thing. If you are more than about 10 seconds into the track and hit back, it returns to the beginning of that track, otherwise, it goes to the previous one - the net effect being that two backs take you to the previous track if you are into the current one.
I took this logic from the aforementioned old box behavior.