Since Steam = DRM, one just cannot say "DRM-free on Steam". It's like saying 1 + 1 = 3
You made a statement. Now you have to back it up with some facts.
What about non-optional feature of steam makes it DRM?
That's a "poor man" form of being DRM-free? Valve aren't some amateur company. In order to make DRM-free offerings their games have to be downloadable as explicit packages without some "copy that directory and you have a chance it won't choke if you run it elsewhere without a Steam client". That's not normal - that's like dancing around a service which doesn't attempt to be DRM-free. Even their official backup tool (which Seam offers) can't reinstall the backup without their own client and connecting to your Steam account. That's not DRM-free in my view at all.
But that is exactly the same with GOG.com for most of their windows games. They are msi files, meaning they are using the windows installer. Just because the Steam-framework does include an installed does not mean that the game contains any form of DRM. Or if that fits your definition than msi-install-files include DRM as well. Sounds like a silly definition to me. And more important it is a meaningless definition, based an principles and not practise.