It was because of a short term black friday surge in sales on other games in top grossing. If you noticed, the other games in the top 10 shifted into the top 20 and are slowing shifting back into the top 10. Will be top 10 grossing game probably by tomorrow night.
There's a lot of chatter that MSFT will be buying out Gluu now that they proved they could provide a top grossing hit game. Deer Hunter has been a top 10 grossing game for over a month, probably has made Glu over 30 million dollars in revenues alone.