Right, but a store with DRM can effectively prevent me from playing the games, that's where my ownership effectively ends.

With GOG, there's no DRM. So in all senses except some weird philosophical context, I do own the game. I paid money and received a file(s) that I can relocate, make backups of, burn to disc, archive, etc.

You could argue that if they revoke the license and I continue using the file that I have on my computer, that I'm now committing piracy, but that's getting into a big technicality