Audio cable not needed for a CD-ROM?

Everytime I have built a new computer ( and I have built three P3), I made
sure that I connect one end of the audio cable into CD-ROM, and the other
into an appropriate connector on the mother board, so that I have the audio
for the music CD's.
Last month I have built a Pentium4 computer (Win XP), and simply FORGOT to
install the audio cables (3-wire cables: red,white, black wires).
Nevertheless both the CD-ROM and the burner play music CD's!
Question: are the audio cables needed at all?