The Enigmatic T replied to someone in the forums about that. If I'm remembering right, he said that the entire soundtrack comes with the game if you get it from the developer.
Maybe GOG has the game with a short soundtrack as part of the deal for making it DRM free? Since it's unimportant to me in comparison to the game, I'm happy with the deal from GOG.
Everyone should go look at their Spring Conference Video (you can skip about half of it if you're not interested in The Witcher 2). If these guys keep this level of dedication to their standards and to gamers, all I can say is Long Live GOG! It's certainly a refreshing contrast to the news about the Worst Company in America.
Love the hat, T.