Yesterday I noted that the incredible popularity of Guitar Hero (and its new cousin, Rock Band) has helped to spur sales of the “real” instruments in music stores. While the evidence isn’t yet conclusive on that front, there’s no questioning what the games are doing for the digital-download business…That’s right – Guitar Hero is a more efficient way to sell your music than iTunes. But put the two streams together is a powerful combination…and we’re talking about Legal downloads. Who knows what the effect is in the P2P world?…