Interesting, I understood it fine. He sais he has a 5.1 surround sound setup and he is asking if its normal when you open up a program such as windows media player, and play a song, that the rear speakers dont output sound. But in games and tests, they output sound fine.
To answer, yes it is normal. Most music is recorded in stereo. You could find songs recorded in 5.1 surround sound but thats not easy. Some speakers and some programs allow you to take a stereo input and make it 5.1 output. Try googling for a few.