The Beatles: Rock Band may have trumped Guitar Hero 5 in terms of both unit sales and actual revenue, but less consumer interest in both franchises has actually dragged down game industry sales overall by about 50 percent. Gamasutra dug into sales for both franchises across all consoles—including downloadable song packs and new game releases—finding that as of September 2009, the brands have generated $373 million less worth of revenue than they did for the same time period in 2008.

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In context, NPD says game software sales are down by $720 million overall for the first three quarters of 2009—meaning the Rock Band/Guitar Hero sales slump accounts for roughly half of the total decline in game sales industry-wide. While that’s a sobering statistic for parent companies MTV and Activision (NSDQ: ATVI), respectively—as they’ve been staffing up their music games teams—it’s very bad news for the game industry ecosystem, from the ad agencies that rep the brands, to retailers like GameStop and Amazon, since that means there’s less money to be made by everyone.