Pheace: This is why GOG has been expanding it's market.
Frankly, I wouldn't be surprised if this was GOG's plan all along. I think they had always wanted to release modern games as well, but started with classics because:
1. It was a niche that nobody else was filling, not even Steam (for the most part).
2. They were already used to selling older titles from their experience as a distributor in Poland.
3. It was much easier to convince publishers to release their older games DRM-free. That way, they could gradually get them used to the idea of releasing games without DRM and make it easier to convince them to release newer games in that fashion as well.
I guess you could say that GOG used classic games as a way to establish the audience and publisher/developer connections necessary in order to start selling DRM-free modern games in the first place.