Even with an almost four-year head start and recent increase in downloads, music sales totals from iTunes have finally been surpassed by app downloads, says Asymco's Horace Dediu. The milestone reflects the incredible popularity of the iOS App Store, which had sales pass the 15 billion mark last week. Apple also reported 15 billion in song sales during the recent WWDC, but began selling songs three years and 10 months earlier.
