1. Is it needed to have the Steam client app installed on my computer in order to download, install or run these games at least once before taking the game folder to a different machine?
2. If not all, can you please point me to the games that don't need the Steam client at all, even for download or first installation?
3. Before becoming portable, do these games need an internet connection for validation? Understand I'm not asking if internet connection is needed to download the games (which I've seen many people are clever to point out), I want to know wether they validate ownership over the internet after downloaded, or if I can shut down all connection to the internet if I want to.
There, perhaps if someone could answer those directly instead of making excuses as to what is or isn't DRM I'd be happier and you could even paste it to the OP as a FAQ.
So, I'll try to answer as far as I'm capable. Please note, that this list grew over time in an utilitarian way, so there may be some borderline cases with online activation, CD keys and such thingies.
1. You need to install the Steam client on your PC, there is no way of downloading game files without the Steam Client, because that's the way it is intended to be, as a local game library and management software. The "run at least your game one time" part is somewhat outdated, after downloading the game in the Steam Client, the game files are in your Steam folder and the "finalisation" only makes changes (or not) in the windows registry and installs needed libraries and dependencies like directX etc.
2. There won't be any games as you sadly can't download game files over the Steam web page.
3. If a game needs internet validation, it probable won't ever be portable. Do you mean by internet validation that you only can install the game on e.g. five computers? Such DRM is not on the list. "Always online" games neither. If games need validation to become offline capable, it is pointed out. And yes, after downloading the game (and sometimes running the game in the Steam Client once [maybe with internet]) you can play them without internet on any PC you'd like (as long as you use the game files you found stored in the Steam folder). That is probably the goal of the list but as always there may be mistakes.
About the topic "internet": Some games can be played offline on another PC without Steam, but the game only offers maybe 30% of the gameplay content without internet connection. If so, it's pointed out.
Oh, before I forget and if you don't already know, the list on page 1 is a bit old, a newer (and hopefully better) version can be found here