Among the most significant changes with this year’s Elements releases has little to do with new features but instead concerns the ways users purchase and own the software. While prior versions of Photoshop and Premiere Elements have been lifetime licenses — the user buys the software and then owns it indefinitely — this year’s release has moved to a three-year license term.
The same software purchased digitally doesn't magically become a "service". Coincidentally, you can absolutely download and backup all your GOG games and then "own" them the same way you own your old CD ROMs.
"In the very unlikely situation that we have to stop running GOG we'll do our best to give you advance notice, so that you can download and safely store all your DRM-free content." - GOG user agreement.
The same thing is in the terms and conditions for each of your old CD ROM games. The point is that they can't physically keep you from using the DRM free software that you backed up locally.
The perceived difference has nothing to do with the game being a "service" or that perpetual licenses are not economically possible for "services" but with the fact that by the power of the Internet companies now have a way to brick your stuff remotely. And you accepted it when they put it in instead of voting with your wallet. Because you wanted Half Life 2 just so so so badly.
They're doing it because they can, not because they have to.