Well, I never used Steam preferring DRM free distributors like GOG, so I can't say much about Valve in this regard except that I know that Steam uses it :) It's unfortunate that they are too engrossed in DRM as much as preventing their games form being distributed by DRM free channels.
Valve is not "engrossed in DRM". They have the most lenient DRM that still qualifies as DRM, and the only objectionable aspect of it is the theoretical inability to install a game without access to the Steam servers. Valve's "DRM" scheme has imposes fewer restrictions on the user than most EULAs, and pretty much never gets in the way of legitimate usage. The fact that they don't want to sell their games without Steam is a business decision that is quite unrelated to the DRM question, and more related to their profit motive and the other services Steam provides that vendors like GoG don't.
What don't you like about Steam's DRM system? Does it in any way inconvenience you or restrict you from doing something reasonable with your purchases? Or are you against it for the mere reason that it's been called DRM? Based on your comments, it sounds like you might be trying to make a principled stand without being fully informed, or else there's some nuance to your principles that isn't yet clear to me.
Offline mode has made me realise just how easily DRM means denying me access to my own computer.
- need to be single-user admin with saved password
- didn't know that before? tough! you're locked out from all games including DRM-free ones
- happened again and still can't get offline mode? tough!
- support limits how big a message you can send so I couldn't send complete info (not that they looked)
- support promotes racial hatred, closing issue with poor English and telling me I didn't do what I did.
- follow up support also closed.
- considered small claims court but was convinced it really wasn't worth it.
lesson learned: There is no such thing as "friendly" DRM. When the system decides you are wrong, there is no recourse
 Unless you're a famous blogger, have a personal contact or other out-of-band means unavailable to the masses.
I don't think any clients from Steam or other distributors need to run in order to install or play some game. And as the other commenter pointed out - you don't want suddenly to lose your whole collection if Steam terminates your account.
This looks interesting. So one can get the installers for these games through Steam and use them without running their client and etc.? I thought all their games require the client running and it's already DRM for me which I don't accept.
Is there an easy way to filter games by this criteria on Steam itself?
Unfortunately no Steam uses its own package format, so it must run the installer the first time to get steam to unpack it. Steam provides DRM but it is up to the author of the game to use it, their own, or none as they see fit. And no Steam doesn't provide any clues as to what DRM is used by a game.
It seems like I have run across other games that use secuROM but don't mention it. I don't know if it was because that was before they added the listing or because there was no restriction like the activation limit.
Well, Valve owns Steam, their publishing arm/store/DRM. And like EA now sells their games with their online store/DRM "Origin", Valve does the same with theirs, Steam!
Yeah, they get more by shoehorning people into Steam than they would lose from not selling DRM-free versions.
There may have been a point to stop this from growing into what it's become early on... But it's too far gone to be broken free of save a major scandal. And even then, it'd probably take a few. It's just by far and large a non-invasive tool. They've worked out many kinks.
I'm not saying it's perfect, nor am I saying we should be happy with it. But it's avoided the major problems most other DRM efforts see in "making things more difficult for legit users than pirates". I haven't had any issues with any aspects in years.
CD Projekt Red who own GOG naturally distribute their own games through GOG, but note that they as well distribute them through Steam. I see no clear reasons for Valve to restrict the distribution of their games to Steam only. Yes, historically it came with this not very invasive DRM, but there is still no reason to keep it forever, since DRM has no good reasons to be used altogether.
I understand that Valve can be already too involved with game producing companies which still have backwards thinking that DRM is a must. But Valve can start pushing them to drop it, instead of being passive.