iTunes costs $1.3 billon per year to run
An
Asymco analyzed recently announced numbers like the total number of songs, movies, TV shows, apps, download rate, iTunes accounts and how much Apple has paid out to developers. They put these numbers in a complex formula and estimated that Apple's monthly content margin cost for iTunes at $113 million, which is more than $1.3 billion per year.
That's a lot. It looks like all the iTunes profits go right back into its maintenance and expansion.