If you're interested in this you might also be interested in a talk that the developer of Fortress Craft gave. Fortress Craft is (in its simplest form) a clone of Minecraft for the xbox 360 indie game thing, he gave a talk at an event a few weeks ago and he explained all the sales figures. It's the biggest grossing game on the indie game thing so far.

http://www.fileplay.net/channels/iseries//13607/fortresscraf...

He starts talking about sales at 16:00.