Earlier quoted context omitted.
You can only be offline for a set amount of time with Steam (last I used it), and the check is made before you go offline.
That's a different thing from what OP is saying, they're right that Steam doesn't automatically enforce any DRM. It does provide the mechanisms but it's up to the devs whether they use them or not. In lots of cases you can just directly run the executable, especially for indie games. Source: am indie game dev
Source: Have used Steam pretty much since it was released and also worked with SteamKit for a project or two.