Navagon: For the people who have bought everything on GOG,
nothing is exactly what should display. Maybe just a "Thanks! You're wonderful! But seriously now... Come back next week. That's next week. Not tomorrow."
No it isn't. For one thing, continuing to display the products is helpful given the fact that those people can still gift games. Thus, a constant reminder of games that are available can help when it comes time for such people to gift games.
Further to that, other people may be viewing the PC/whatever device they are browsing from at the same time and can then see a selection of games on offer. If they just saw an empty space, they'll get the impression that the site has nothing to sell. That's bad for GOG's image.
The very basic point here though, if it ain't broken, don't fix it. And the display of a few games you may already own, isn't "broken".
MountainMan: There are people who have bought every game this site offers? Seriously?
Yes.