komoto: I think there is some room for debating some small aspects of what DRM is, but some of the people commenting in this thread clearly haven't got their head around the well-established basics.
By that strict definition of DRM then only some Steam games have it and others don't. If you can execute the game outside the Steam client, it doesn't have DRM. The actual download client is irrelevant since the flows are identical. It only at execution time that it matters. Since you could execute some games w/o the Steam client, those are DRM free. That you might choose to also execute them through a flow that checks your user id is irrelevant to the game having or not having DRM itself. Because the game itself is not wrapped in a DRM. Usually at this point, I make the move to the white board where definitions and consequences are written out so that the discussion doesn't get sidetracked by redefining things mid-process. But I feel I've put out the subtleties I'm trying to express so I'll let this reply stand as a finale.
In fact, how the general person uses a word is more important than what you or I think the definition is or what you look up a definition to be (I found this hard to accept for many years). Unfortunately (or fortunately) usage defines language, not a dictionary or a web site. No worries though, because N years ago, I was right were you are now. So while you might not get away with a Minotaur definition, the definition that my mother would give to DRM is more accurate than any technical definition that I or you might use. Such is life. (You have no idea how many years I wasted trying to fight the popular use of the word "hacker" (I was wrong)). [by the way 'letter of the law' is euphemism in the U.S. that generally means "in the strictest sense" it doesn't have anything to do with the law (as in judges and lawyers)]
In any case, GOG manages your digital rights via the license which restricts you from handing out copies. If you do so, you might as well have downloaded the game from a torrent. Steam manages your digital rights via the license which allows you to have access to the games.
These licenses are not DRM technologies, but they are within the entire system of managing your digital rights for each service.
(Besides the initial login which does seem to satisfy the requirements to be a DRM technology in both cases) The DRM technology of Steam is the a license check for most games when you run them (assuming you aren't in offline mode).
Beware relying on what is "well-established", because that always involves dependencies on assumptions that may or may not apply in various contexts. :)
Also, I don't think I'm saying what you generally seem to think I'm saying, but I could be wrong.
again ymmv (ie, all this is just me 'talking' and I could be horribly wrong (which wouldn't necessarily surprise me)).