@CK0: Whats so special about the music files ;-)
According to
W3Schools, the Audio tag functions with different audio file types, depending on the browser.
.mp3 files should work with IE9, Chrome and Safari.
.ogg files should work with FireFox, Chrome and Opera.
In a nut-shell, the audio files are there for cross-browser compatability.
However, I have yet to see the Audio tag working in IE9 at all. Perhaps I'm missing an update.