Usually the basis for copy protection to prevent CDs playing back on computers is to make some of the data on the disc unreadable. Computer CD drives have a lower tolerance for errors than home audio players, since they need to reject bad discs (and data) rather than the copy the aim of the home CD player which is to play back the CD if it's at all possible. To do this, audio players will interpolate data and take a guess at what should be there. Since these drop outs are relatively short in duration people will not usually notice them. Computer drives don't do this because guessing is not really an option.
I saw a site where a guy had compared the errors between one of these protected discs and a non-protected disc and the difference was huge, as I remember thousands of times more errors from the copy protected CD. CD drives can tolerate some problems because they use error correction which lets them figure out what the data is even if part of it is lost. At some point you will lose data though, in spite of this and this means audio information.
How close to this line the manufacturers are tiptoeing I can't tell without actually having one of the discs to disect, although I would guess that they have crossed right over the line. This is just a gut feeling though, so take it with a grain of salt.
Greg