"Audio Reserved" drives

I recently went to a flea market looking to replace an old DVD burner.
Several dealers had OEM Lite-On and LG drives, and on closer examination
I noticed something I hadn't seen before. Stamped right into the metal
cover of the drive housing near the analog and digital audio out headers
were the words "AUDIO RESERVED". Further, the labelling that gives the
pinouts and jumper positions deliberately omitted any mention of the
two normally-audio headers. What gives? Of what importance would
disabling audio output be to an OEM buyer?