In this article, which misses one major economic element of the current decline (that the previous high was partly based on the 15-20 years it took music lovers to be able to afford to replace all their vinyl on CD) the following comment comes near the end:
“By mid-2007, when the majors realised that digital downloads were not growing as quickly as they had hoped, they landed on a more adventurous digital strategy. They now want to move beyond Apple’s iTunes and its paid-for downloads. The direction of most of their recent digital deals, such as with Imeem, a social network that offers advertising-supported streamed music, is to offer music free at the point of delivery to consumers.”