Part of an email I just received from them:
Dear Reader Store Customer,
The publishing industry is turning a page and so are we.
Beginning April 1st some major publishers will be instituting a change in the pricing of eBooks, which puts decisions on eBook pricing firmly in their hands. As a result, prices of bestsellers and new releases from these publishers will be changing on the Reader Store, and during the transition time, some titles may be unavailable. Although most of these eBooks will be priced from about $12.99 to 14.99, there will not be a broad pricing change across the Reader Store. In fact, new releases and bestsellers from other publishers will still be priced at $9.99.