Gede: Aren't those games that are only checked at download time? So, you can download, backup on your hard drive, and play at will forever from that copy? No more need for the Steam service or Steam client?
vv221: As far as I know, you need the client to install them. That you are able to take the installed data out of Steam’s claws to make a backup is nothing more than a hack, not a feature.
To compare with GOG stand-alone offline installers.
If the installed game makes no effort to validate anything ever, it's, IMO, not DRM.
Though I agree it's pretty inconvenient that there's no clear way to "install" it again without the phonehome client.
Steam does have a feature to "backup" or export the game on one machine and import it again on another, but my bet is this process phones home.
Basically at that point I think we're in crappy implementation territory. Like does the game not work if you move it around, and if so, what files would you have to edit to change the paths? I'd bet big bucks you could just drop the fallout install on another computer in another dir and have it just work, and at the worst case it would work if you just use the same path.
However, some game that installs bits of itself in bizarre locations (like weird services or whatever) would not be reasonably portable, even if not trying to apply DRM.