“Three billion applications downloaded in less than 18 months—this is like nothing we’ve ever seen before. The revolutionary App Store offers iPhone and iPod touch users an experience unlike anything else available on other mobile devices, and we see no signs of the competition catching up anytime soon.”
Iphone and Ipod Touch being the chief culprit for this enormous number. Apple has made so much more money off data distribution, and it's amazing that they had to foresight to plan for it.
Is there anything close to the success ITunes and App store have enjoyed in terms of data distribution? The only thing I can think of is Amazon.com Kindle e-books. But Apple has cornered the market on TV shows, movies, songs, mobile apps, etc.
This is one of the reasons why Microsoft's Zune HD, while an amazing little device in its own right, will struggle to be as popular as the Ipod Touch. The plethora of apps for virtually anything gives the consumer an amount of freedom that the Zune does not.