The Rock Band franchise has surpassed $1 billion in North American retail sales in 15 months. This is according to figures released by the NPD Group.

MTV Games, Harmonix and EA must also be pleased as punch with the 40 million songs that fans have paid to download since the game was first launched in November 2007.

Here are some more interesting Rock Band facts courtesy of MTV:

• According to NPD, Rock Band was the number 1 title of 2008 by revenue across all game genres.
• There are now 614 songs offered via the Rock Band platform, both on disc and in-game music store as at March 2009.
• 269 different artists/bands offered via Rock Band franchise as at March 2009.
• Over 40 million paid songs have been sold via download since Rock Band launched in November 2007.