The problem is that most of those protected disks also don't play (or don't play correctly) on a regular audio-cd player!

True, but only for SOME audio-CD players.

They're trying different schemes in an attempt to find the magic bullet: The scheme that makes the CD play in the most consumer CD players as possible, while still preventing the computers from easily copying it.

The one that I saw did a pretty darn good job of it. The tracks appeared to be data tracks to the ripping software, so it basically said "hey, this is a data CD, I have nothing to do." Whereas an audio CD player just tried to play whatever it could, and worked without a problem. Very clever, guys, too bad you didn't count on certain CD copier programs which rip raw data and subcode channels and write convenient cue sheets for you.