In an article that talks about the various industries Apple is involved in (and comparing them to others if they were separate businesses), Asymco's Horace Dediu points out that Apple's iTunes business -- all by itself -- is a monster corporation. It has an estimated gross margin of around 15 percent, is steadily growing over 30 percent per year and may become Apple's third-largest "leg of the stool," passing the Mac business at some point this year.
