I'm not so sure the quality is affected. The older copy protection only required yo to enter a serial number before installing a game, and an increasingly longer one at that. That has no effect on gameplay. However, with some of the newer copy protections, I know that the game (or the copy protection for that matter) checks for the disk in the CD-ROM drive several times during game play, thus increasing loading times.
Many people don't like playing with the CD in the drive because it puts wear on the CD, and with enough wear on a CD, the game can be rendered unplayable. This is a reason why many of us here at CDFreaks advocate fair use and the ability to make a backup for personal use. That way, the original isn't worn out, and only a cheap CD-R(W).