Note, if you actually look at that list you'll see it's a very loose interpretation of DRM. All of the games on that list work without any kind of phone-home security check, or unlock code, or anything like that. The list is stuff like "getting the DLC requires a third party account". It's definitely a list of things people don't like, but whether it is or isn't 'DRM' is not so clear cut.

GOG's official position is that the store doesn't allow DRM at all. They describe what they mean by DRM on that same page, and it sounds fairly reasonable; but its certainly understandable that some people would prefer a stricter set of rules.