I'm also wondering why we are so worried about the difference between DRM and copy protection. The topic is Steam. They use DRM, and a part of it is prevention of unauthorized use. This is very mild stuff, and does not mess with your system. Other parts:
- game store
- download service
- online services
- anti cheat software
All this is "DRM". It enables you to install Steam on any Windows/OSX PC, log in, download all your games, and start playing.
You can always put your games in offline mode. Then they can't touch you. Online services are never in your control, so I don't see how using "DRM" makes it worse.