adaliabooks: I imagine it's just a difficult proposition to get developers or publishers to agree too.. there's not much in it for them.
As I remember the original batch of games they did it with were all (or mostly) from Russian Developers and it happened around the same time as the Russsian language and pricing were introduced. So I imagine it may have been intended as part of a "stop pirating games and buy from GoG" initiative aimed at the Russian market (at least I understand that's part of the reason for the very cheap prices Russia gets for games)
That seems about right, I remember they did this with STALKER. I didn't take the offer, because I wanted to buy CoP from them, but if they were doing this with Codename Panzers I'd be sure to take advantage of it. As it stands I'm going to have to buy it from them. Not that I mind, honestly.