“The provision of developer revenues means we can determine the pricing of apps,” Dediu writes. “The pricing of apps and the download totals allows us to determine the revenue of the store. Using the time stamps of the reports allows us to determine these quantities over time.”
Dediu writes, “The iTunes economy defined as gross revenues transacted through it is now about $12 billion/yr.”
Much more, including the usual fine graphs, in the full article here.