Copying your install directory and manually editing the registry to make your install function properly depending on the game, isn't something any ol' computer illiterate moron can do themselves. I can't tell you how many times someone has been unable to do so simple a task as to set up a Sins mod, it's beyond a great many people.
No need to edit the registry, just download steam on any computer and copy the old steamapps folder you already have on a usb stick or whatever. Not much on a computer that is more simple than copying a folder. A lot of people that dislike steam are just misinformed in how it works and all the features that actually benefit the consumers freedom to use their software. A lot of people think it is harder to do things than it actually is, just as in your example of requiring a registry edit.
Many games on steam dont even require it to be installed after downloading if you really dont want to use it. Crusader kings 2, Europa Universalis 4 and pretty much any other Paradox game, FTL, Kerbal Space Program, Wasteland 2, and even a few UBISOFT titles, Farcry 2, and Assassins Creed: Directors cut for some reason. I own all those games have personally tested it. Plus many more that you can find other people have tested. Its actually something that I wish Valve would mark on their store page which games are DRM free the same as they do with games that use a 3rd party DRM. Those DRM free games work the same as any game bought off GoG.
Steamworks is also the lightest of DRM to be basically not be one. As I said, a single login once every X years you upgrade your computer if you really dont want to be online is pretty minor access control. I would also put Steam in the TOO BIG TO FAIL market right now. 125+ million users are mighty valuable. Steam would be sold to Microsoft, SONY or Google before it would ever shutdown.
I just buy the game where the best deal is. Both CDProject RED and Valve actually have very similar values and ideas when it comes to DRM. They both came about because of the Starforces and SecurROMs of the past. They are both companies that prefer to give the consumer more rather than take away.