Which is not DRM at all.... There are fully working no-CD cracks available if that bothers you.
Sorry I assumed that it was some form of securom drm. I thought hypothetically that if I were to lose my game, or break it, I would lose my right to play it and have to purchase another physical copy. Unlike gog games were have no limitations and can legally make unlimited backups.
You can back up physical disks. What makes digital rights management an issue is that your rights are physically managed. You may disagree that requiring a CD is forcing you to play it from the PC that the disc is in... but I think you would be in the extreme minority on calling that any sort of issue. There is nothing to say "you have already installed this", or "this is not the PC you bought this for", or "there is no internet connection to verify ownership"... etc. ... which is what DRM does. I'm on my 5th PC since I bought this game and have reinstalled dozens of times since I bought it (all legally). The publisher has no clue because there is no DRM to inform them or to prevent me from doing it. (I also don't use the disks, I use a disc image with a no-cd crack... something that would rarely (if ever) work where real DRM is present.