Maybe you could find some answers in this link.
Its german, though.
http://www.pcwelt.de/ratgeber/software/15859/4.html
In concluding words:
The CRC is calculated on basis of the digital information stored on each disc, which stay the same, unless physical harm is done to the disc.
But it depends on your drive which results you get, because it calculates the pre- and post-gaps which are insatlled by the drive and may differ from read to read into the CRC.
The more equal the CRCs, the better quality is your drive.
@halcyon
In Germany usually the RecordLabels have CDs without CopyProtection. Although they never go out to stores they usually replace the copy protected one with a cd w/o copyprotection, but only if you ask.
Greets, Tick Raw