I have asked Steam about the possibility to copy game folders as DRM-free backups and this was their answer:
"1 Message by you on Wed, 15th Feb 2012 4:30 am
I have been told that some games allow for DRM-free backups by just copying around their installation folders in steamapps. what I mean is that you can copy the installation directory of a game in steamapps folder and then you can play from that copied folder in whichever computer you want regarless of having the Steam client installed or not. For example, you can do this with Binding of Isaac.
Is this practice allowed by you?
Thanks for your time.
2 Message by Support Tech Toby on Fri, 17th Feb 2012 3:27 pm
Thank you for contacting Steam Support.
To install the game on your computer, you must have the Steam application installed and a valid internet connection.
To install Steam, please see this page:
Get Steam Now: http://store.steampowered.com/about
After Steam is connected to the internet and the game is fully updated, you may set Steam to offline mode using this guide:
Title: Offline Mode
Once properly set to offline mode, you can disconnect the computer from the internet.
Please let us know if you have any further questions.
3 Message by you on Sat, 18th Feb 2012 4:25 am
I know the details of the offline mode and how to install games with the Steam client. My question is if it is allowed to backup the install directory of a game directly from the steamapps folder and then use that directory independently of the Steam client. It would be a fully working (in the games that allow for this) Steam client free version of the game.
4 Message by Support Tech Toby on Sat, 18th Feb 2012 8:25 am
As previously stated, you must have the Steam application installed and a valid internet connection to install and play the game on your computer.
If you have any further questions, please let us know - we will be happy to assist you.
So, if I understand it correctly, they don't allow this practice. It's kind of like GamersGate DRM, easy to skip, but still officially against the rules (laws?). I may buy some Steam exclusive games from Steam if the developer explicitly encourages this practice and I really, really want to buy that game, although I would still show my disagreement with the developer and these games would still be on the bottom of my priorities. In my opinion this is just a "dirty solution" no different from cracking a game and only solve my issues on a game by game basis and only partially.