The difference with GOG is that with Steam games -- even those that don't use Steamworks -- you need to use Steam AND have a working Internet connection to install the game, so you are not truly separated from Valve's ecosystem. With GOG, you can download all the games you own, back them up to a portable hard drive, and then you can play all the games regardless of your Internet connectivity or GOG's continued existence, even if you change or wipe your computer. With Steam, you can only play these "DRM-free" games until you next need to re-install them for whatever reason.
Back in, say, 2000--2004, a game that needed the Internet to phone home during installation (but not every time you play the game) would have been considered an unacceptably intrusive form of DRM by some. It's funny how the public perception of DRM has changed so much that phone-home-on-install is no longer considered to be DRM at all. Well, it still is, because it's a server that controls your ability to use a product you have already paid for. Granted, it's relatively mild DRM, but it's still DRM.
I suppose that once you install a non-Steamworks game, you could manually grab the files and zip them up and archive them, but Steam doesn't make it easy. If you had, for example, used Steam's "back up game" feature, you would find that it requires a phone-home to restore the backup. In addition, Steam doesn't make it easy to play these non-Steamworks games without using Steam. All the Start Menu and Desktop shortcuts launch Steam with a particular game ID, not the game .exe directly, so using these shortcuts either requires that you are signed in to Steam, or have explicitly put Steam into offline mode. It's actually quite difficult for the average user to figure out how to run these so-called "DRM-free" games without Steam. So yes, GOG.com is absolutely more entitled to be praised as offering DRM-free games.