As Enebias mentioned above, this is semantics to a large degree. But to answer your question i could do all the above, except the 'legally' part. Heck even Amazon have been caught selling GOG exe's!

But the real point is about having full control of my game copy. I can install it anywhere i want without restrictions. I can play my game anytime, anywhere in the world without having it have to connect to a remote server.

I can mod it, patch it EXACTLY as i like without a third party stepping in to say hold on, but no. If GOG went out of business it would not stop me playing those games right at that moment, as once i buy and download a game on GOG i no longer rely on GOG to give me access to that game. It is mine in the full sense of the word.

It's quite simple really, the difference and value GOG offers over services like Steam. Worlds apart in relation to being on the gamers side first and foremost, business second.

Sure Steam saved PC games back when consoles were the big show, but Steam has only ever really been interested in itself. There is little altruism in what it does or what it says, except perhaps when external threats to it's business come along (MS Store etc and Gabe's correct statements on why this is bad). If Steam was fully for the gamer it would operate more like GOG does.

Steam is about BEING the control. GOG is about giving you the gamer the control. Very different psychology.