I’d say Halo should have a Haloween event.

I don’t think “weasel words” is the right term here.

You own the GOG games like you own a book you bought, and like you don’t own a DRM-crippled book, even though you might be entitled to read it under certain circumstances. The difference between downloading an installer and downloading a game on Steam is, the installer will continue to work even if GOG folds or decides they don’t like you anymore. But if Steam blocks your account, all the games you bought are gone, and Steam is fully in the right to do so since you don’t own their games.