MysterD: Things get more tricky if there's some files only server-side, Saves Cloud-side, and/or stuff of that sort. Probably would be a pain for hackers to reverse-engineer, to work offline.
Gamers are used to this treatment as they have all of these shiny features in their client-app on PC or on their console - Achievements, Online Co-Op/MP (if supported), Cloud Saves, etc etc.
Gamers often can't wait - and just buy stuff ASAP at $60-70. A lot of us here on GOG might not be of that club, but a majority of gamers do buy stuff on Pre-Order, Day 1, Week 1, or not too long after.
Dev's and pub's seem to be training gamers for the inevitable streaming-only gaming take-over, whenever that horrible inevitably comes.
So gross, man. People are rightfully appalled at the manipulative phenomenon of "grooming," yet don't realize a more benign version of that is happening to them when it comes to accessing media.
As for buying stuff day 1, I have no problem with that if it's DRM-free (actually DRM-free, not just advertised that way by GOG in between pushing their proprietary client Galaxy that Manages the Rights to your Digital media).
I do see where day 1 buying results in some of "early adopters are beta testers and the complete game doesn't come out in a working state for another year or two" mentality, but I think that's a separate issue beyond DRM.