XBox360 users buy 3.8m music tracks a month

"In a statement designed to highlight its self-appointed status as the "preferred stage" for music-based games "Guitar Hero" and "Rock Band," Microsoft released data showing gamers, on average, buy 3.8 million songs a month, for either game, and have bought more than 45 million tracks for both to date, across all installments of the respective franchises."
Source: Billboard, 20th October 2008, citing Microsoft