Re:Requirements for DRM in HTML are confidential
by shmerl on Tuesday January 14, 2014 @11:33AM
(#7057915)
Running the game and installing it aren't the same thing. Some Steam can can be probably trivially copied (the game directory), and are backup-able that way, but you never know which ones, and which require more steps for installation. Steam also doesn't mark any such details on the games before you buy them.
These settings are up to the game developer themselves. You are right about the offline mode, but it does not apply to all games.