Tim Cook announced during Apple's most recent earnings call that iTunes is now one of the main drivers of the company's business. Because of Apple's crazy-popular hardware, it's easy to forget its focus on e-commerce by selling books, movies, and music through iTunes.

However, all it takes is one look at a chart comparing the number of iTunes accounts versus active Amazon accounts to see just how big the iTunes community is.

In fact, iTunes has nearly quadruple the number of accounts — and thus, credit cards on file — as Amazon does. This gap feels stunning, especially considering how much more than just movies and music that Amazon sells. Apple's wealth of credit card information could end up giving the company a huge advantage if it eventually decides to work on some sort of mobile wallet.

Horace Dediu, an industry analyst, tweeted out this chart: