Amazon? Not playing around with publishers when it comes to ebook deals. Penguin's contract ran out on April 1, so Amazon can't sell their ebooks. So Amazon's cut the price of Penguin's actual hardcovers to $9.99 ebook pricing.
Which, one, shows just how cutthroat Amazon will be on pricing—a lot of the $9.99 hardcovers aren't even bestsellers, so Amazon's flat out giving away money—and how determined they are to move books in volume and retain customers using price as a blunt-force weapon. Also, it aggravates the piss out of Penguin, while avoiding the publicity fiasco that was yanking Macmillan's books out of their store entirely when they weren't playing ball.