The result is that a disk driver like sys/dev/scsipi/cd.c can not create 
   its own default label while still supporting `normal' disklabels to be on 
   the disc. It can't determine if there is a label on the disk or not.


that doesn't matter.  your change broke other behaviour.  that's
why it was backed out.  it's true that there is a problem with
disklabels and cd.c but blindly whacking around it isn't going
to fix it -- this problem also affects sun cdroms that have sun
disklabels, but in my minimal hacking i only managed to break
other behaviour.