Wow, that was fast. Just a minute ago, it seemed Guitar Hero was supporting the entire U.S. economy. But sales actually dropped 22 percent last month and it's even worse for Rock Band: down 52 percent! All of which bodes poorly for Activision's much-hyped next release, DJ Hero. Of course, there could be a very good reason for these steep declines — everybody already bought the games. [Business Insider]