Just test both GOG's and Steam's version of Thief™ Gold on Windows 10. GOG's version runs the FMVs without the need for any fixes or whatever. Steam's version doesn't. Other than that, both games seem identical.

GOG 1 x 0 Steam

I've got a few games on both Steam and GoG

The only minor difference and its a tiny thing

Playing the GoG version of a game does not boot my children off when they're playing an entirely different game from my library on another computer, Steam does.

Its a trifling small thing.

Same here. Not because I bought them on Steam; they were "boxed" versions. I just uninstalled them after getting them on GOG.

It is my dream (one shared by many) to finally have every game from my Steam library Here on GoG
96 games -23 from valve (i can live with out the) - 18 already here - 6 safe elsewhere. 49 games to go.

I'm sure it'll remain a dream. Too many companies just don't want to go DRM-free. Maybe 20 years from now you'll have 10 to go (we can dream right? ;-)