When you purchase , you are not just getting a digital download key. GOG prides itself on archival preservation. Here is what the offline backup installer (about 6.8 GB) contains:
If you purchase Fallout 3 on Steam right now, there is a 50% chance you will spend an hour editing .ini files and downloading third-party fixes before you see the title screen. If you buy it on the Epic Games Store, you might find it won't launch at all without a fan-made "anniversary patcher." Fallout 3- Game of the Year Edition v1.7.0.3-GOG