The article is some wrong:
In Steam you need to go to offline mode if you want to play without internet, but for going to offline you need an internet connection first (and update all games and software), if you lose the internet, you can't go to offline mode, it is not like "hey! my internet is gone but I can play my steam games"..
And so are you (wrong), at least from where i am sitting, disabled my Network card, booted steam, selected "offline mode" and played some Rage.
Afaik the only requirement is, that you need to have played the game (activated it on your machine), and it needs to be up to date (how that works since , well how should it check). But considering that Steam usually updates the games all the time it's hardly a problem.