3rd parties are responsible for patching games via Steam, and fixing problems that arise from patches.
I haven't had problems logging into Steam since back when HL2 launched. I'm always logged in, and I log in at work. I honestly think Steam is too successful to ever shut down at this point, but even Valve has come out and said they would release a 'patch' in that event.
If you know you're going on a trip and wont have internet, you probably would have already logged in at some point. I believe it will allow offline mode if you've already logged on with that machine. I do not know specifics.
I think you make sense when it comes to separating the DRM and the client. I personally hate almost all DRM. And I think because the client brings other features and it 'is' the DRM I mind it less.
There are definitely benefits to having a system which is lenient and one that publishers back because it prevents piracy. I think Steam fits this bill: As far as I know it does prevent piracy. I have heard about older games (HL2, CS:S) being pirated, but I haven't kept up on any of that. Mostly because I've paid for those games and don't mind the DRM.