Downvoters need to research more.. probing analyst is right..
I purchase ebooks from Amazon, Kobo, ex-WHSmith, Watersmiths (depending on where it is cheapest) and read them all on my iPad and Android phone. Strangely Apple's store has never been the cheapest (at least in GBP).
However, the DOJ is correct. Banning the Amazon app would have immediately brought in charges of abuse of its tablet monopoly, given Amazon's size. So that is a pretty lame defense, they did not really have any other choice.
The most favoured nation clause has caused prices to artificially rise, and price fixing or buffering is cartel behaviour. I saw the prices rise after this 30% commission and most favoured nation clause was added, notably the Zinio mags and The Times in-app subscriptions.
Apple needs to defend the most favoured nation clause they demand. They are free to ask for 30% but not to demand that, even with that cut, the price is also the lowest. The only way to achieve that is to increase prices elsewhere, given the margins involved for the content makers. Remember that it is 30% of sale price and not 30% of the profit made on the sale.
If some competitor, say Kobo, wants to offer a 2% cut, then the price should be allowed to go down by 28% in the Kobo store.
Apple certainly enjoys capitalism, well free markets are part of that, and abuse of monopoly positions isn't.