The Government starts from the false premise that an eBooks “market” was characterized by “robust price competition” prior to Apple’s entry. This ignores a simple and incontrovertible fact: before 2010, there was no real competition, there was only Amazon. At the time Apple entered the market, Amazon sold nearly nine out of every ten eBooks, and its power over price and product selection was nearly absolute. Apple’s entry spurred tremendous growth in eBook titles, range and variety of offerings, sales, and improved quality of the eBook reading experience.
The full PDF can be found here. Apple makes a very good case: If it weren't for Apple's collusion with publishers, Amazon probably would still be an e-book monopoly.