The big publishing houses use new, popular titles to generate a significant amount of revenue - which is why new releases are higher priced than classics or older popular releases - no one in this forum should be unfamiliar with that fact. Which is why many of these are released in hardbound version first with the paperback being released some weeks down stream.
What was happening in the case of Amazon is the fact that the publishers were holding back popular titles from Amazon, because of the pricing model Amazon was using. So Amazon wasn't pricing premium content, just less popular content (which judging from some of the commentary here is a preferred category anyway) aggressively. Since there is a tipping point between price and popularity, Amazon was trying to leverage that to drive traffic and uptake on their ereader devices. The publishing houses had little choice in who to go to for epub format book sales it was substantially Amazon and few other large retailers. This allowed Amazon to use a predatory pricing technique based on their control of a majority of the market.
Enter Apple. They want to be able to provide epub content at reasonable prices (because having to charge a lot for them would slow uptake - witness their approach on iTunes for music). In order to level the playing field with Amazon, they went straight to the source - the large publishing houses. The plan is simple: we support you setting the prices to what you feel is competitively profitable for you, everyone gets the same pricing scheme without favoritism. No one gets to drastically undercut anyone else, everyone gets to play by the same rules.
Not a bad situation unless you are a rabid consumer of "paperback" level literature and have been enjoying Amazon's predatory pricing, and now have to pay a price that allows more money to support less popular titles and writers and allows a potentially more diverse authoring environment. Witness Amazon's scramble to lock down as much epub content as they can prior to the trial. They may suspect it won't go the way they want, so those of you crowing about the loveliness of Amazon's pricing will soon find that those sources they lock down will belong to Amazon to price as they see fit.