Yeah, because the music is stored in the movie file's audio track. It's not used in game.
I'm pretty sure it's in this file, if you've got the patience to download 58 meg of preview crap from before AoM was released: http://www.fileplanet.com/files/110000/118865.shtml(From this article: http://www.gamespy.com/articles/january03/aommusic/)
TheShædøwDåwn
If you're like me, then it's possible you're a clone generated from my stolen DNA. I suggest you turn yourself in for destruction immediately.