Not quite. Steam isn't inherently DRM, it's optional. If a developer wants to release a game on Steam without DRM, they're allowed to do so.
Well, Steam is both DRM and a Content Delivery System. Usually if a company wants to add DRM to their game, they will add it to their source and it will
usually be in both versions, Retail and Steam. Steam's own DRM system is almost always included with a Steam copy of a game though, whether the company removes their own DRM on the Steam release or not. Of course, developers have a choice how they want to release their games, including if they want Steam's DRM applied or not. You can see
here that while some games are "DRM-free" you need to delete the api.dll for it to actually happen, launch a different executable, use the linux copy, use a certain version, and so on and so forth.
So while yes, I agree with you, and you are technically correct, for most I assume they should expect "Steam DRM". Most titles I own are available on consoles too afterall, and they almost always at least have their DRM system in place.