(Version: gnome-mime-data 1.0.8. Not listed in version field.)
This is a bug in GNOME1 and GNOME2.

xmms should be the default application for playing mp3s and oggs.

It is *incredibly* annoying to have mp3 files play in mpg123 - this is a
console app, so after clicking files in nautilus, I have absolutely /zero/
control over my music, and the only way I can stop it is by launching a
terminal and running 'killall mpg123', or 'killall mpg321'. That's if I
knew it was mpg123, which some users may not. Also, there is _no_ feedback
when launching this, so often times I've clicked it twice, expecting xmms
(or some graphical program) to pop up, and then I get the song playing two
or three times at different places in the song. It sounds horrid.

Ditto for oggs and ogg123. xmms also supports oggs. My Red Hat system came
with ogg support by default, and the xmms package on Debian provides ogg
support as well.