US game-industry trackers the NPD Group provided GameSpot with an inside look at the Guitar Hero-Rock Band rivalry last month, revealing that the most recent edition of Activision's stalwart is outpacing its Harmonix-developed rival by a margin of two to one. According to the firm, Guitar Hero World Tour sold 3.4 million copies domestically in 2008, compared to Rock Band 2's achievement of 1.7 million units.

As part of its year-end earnings announcement today, MTV Games' parent company Viacom corroborated NPD's findings, saying in a postearnings conference call that Rock Band 2 has sold nearly 2 million units worldwide on the Xbox 360, PlayStation 3, PlayStation 2, and Wii through the end of December. Nevertheless, Viacom said that the tally came in below its internal expectations.

"The soft retail environment definitely weighed on sales of our consumer products, particularly during the fourth quarter," said Tom Dooley, executive vice president and CFO of Viacom. "This also impacted sales of Rock Band, which has a relatively high price point. That, however, does not diminish the franchise's great success so far. Rock Band was the number-one game title for 2008 by revenue across all game genres, with more than 10 million units shipped worldwide since its launch."

Dooley went on to say that a growing number of consumers are picking up Rock Band 2 as a standalone game, rather than springing for the game's bundle that also includes a microphone, drum kit, and guitar. "This shift will impact our revenue growth, but it will also improve profitability," Dooley noted.

On the whole, Viacom's Media Networks segment--of which MTV Games' Rock Band is a part--saw revenues climb 8 percent during the fiscal year to $8.75 billion. The media conglomerate attributed a portion of its climbing revenues to increased sales of the Rock Band franchise. However, the division's operating income slipped 10 percent compared to a year before, falling to $2.73 billion.