StingingVelvet: The point is that if somehow Steam closes in 10 years people will make sure you can keep playing Steamworks games. Everything else is just principle.
Sure, people can provide cracks and unofficial patches, but they cannot legally distribute game files if Valve were to go poof. So you'd have to install all your games, zip them up and hope they are properly portable. I imagine that would be quite a pain to deal with, if you have a large library, unless someone wrote a script to automate all that too.
Sure people could
technically distribute them, but we have no such right in the eyes of the current law.
Sure we cannot distribute GOG's installers either, but at least we do not have to zip them up or look for cracks. That part is done for us by GOG. If you have a large library, you can use community scripts to automate your long list of downloads and there's no need to install them or manually archive.
While we can
technically do everything that GOG does ourselves, GOG still saves us a lot of busywork and does so legally, so I think buying from GOG is more than just a matter of principle.
Lovstrelfra: This makes me wonder. Do you think if one day GOG were to become big enough to really rival Steam, would the latter eventually stop allocating its resources to ensure that all its games will remain playable in anticipation of the possibility that the storefront might close one day? What I mean here is that with GOG already selling DRM-free games (ofc not all of them, as there have been times when DRMs are still found in some games released here on GOG), would Valve then subtly pass that responsibility to GOG in keeping the gaming community happy with DRM-free games after Steam is no more? That said, there's always the possibility that a different company would just acquire Valve thus preventing Steam's collapse. But still, I'm interested in your opinion.
Should GOG ever grow large enough to threaten Valve, Valve would simply start offering offline installer service to publishers who agree, killing GOG with this one single move. Not everyone would agree, but I imagine those that are already on GOG certainly would. At that point GOG would lose the only advantage it has on Steam.