As we’ve described before, Apple and Amazon come at the e-book
market from different perspectives: Apple sees books as just
another form of content that it can use to sell iPads and other
devices, whereas Amazon sees devices like the Kindle and the
Kindle Fire as ways it can lock people into its content ecosystem
and sell them more books, movies and so on. But both are dependent
on having users locked into their products, and so they make it as
difficult as possible to move from one to the other.