I watched Dave at his GDC presentation for the Shivah and someone in the audiance asked that question and Dave just answered "good..."

the guy was like "oh.. ok.."

I don't blame him if he doesn't want to share that information for various reasons, tho I hope he does as it would be very interesting to know.
You're right about the Minecraft guy he is in the Swedish newspapers all the time because of that, which really brings his games to a wider audience, but then again he really made news-worthy amount of money and I'm not sure AGS adventure-games has potential to come near that, I mean personally I can't play more than 10 mins of minecraft without dieing of boredom but I can still realize that non-story-games always seem to be the answer to profits.
But yeah I can imagine the GR sales must be pretty good, I mean personally I enjoy the blackwell games more (the puzzles there seems more about understanding the story and less about solving silly obsticles) but I cleverly see GR getting amazing coverage (#2 spot on metacritic, whereas Blackwell wasn't even on metacritic at all!) and being a more marketible game.