Why doesn't adduser fix anything?

[Joel Konkle-Parker <jjk3@msstate.edu>]

I'm trying to use XMMS to play cds, and GNOME's Mixer applet to control 
volume. These try to access /dev/cdrom and /dev/mixer, respectively.

Here's the original lines in /dev:

--
brw-rw----    1 root     cdrom     11,   0 Mar 14  2002 /dev/scd0
crw-rw----    1 root     audio     14,   0 Mar 14  2002 /dev/mixer
--

As root, I did:

--
# adduser joeljkp cdrom
# adduser joeljkp audio
--

Neither of these fixed the problem, though. Only when I did:

--
# chmod 666 /dev/scd0
# chmod 666 /dev/mixer
--

did XMMS and the Mixer applet work correctly. Why didn't adduser work as 
it was supposed to? Is this the 'correct' way of letting normal users 
access the cdrom and mixer?

- Joel