That's a different thing from what OP is saying, they're right that Steam doesn't automatically enforce any DRM. It does provide the mechanisms but it's up to the devs whether they use them or not. In lots of cases you can just directly run the executable, especially for indie games.
Steam can work as a dumb CDN for executables, but a substantial number of games do use the out-of-the-box Steam DRM, especially the AAA games GP referenced.
Source: Have used Steam pretty much since it was released and also worked with SteamKit for a project or two.
