Amazon does not set the price; the publishers do. Many publishers set the price of the ebook higher to prevent cannibalization of dead tree book sales. Also,

Amazon does not set the price; the publishers do. Many publishers set the price of the ebook higher to prevent cannibalization of dead tree book sales. Also, ebook prices drop more slowly over time than do their real world counterparts, so higher initial prices allows them to make more revenue from the title. Finally, the higher prices are intended to cover the cost of digital piracy. The prices are estimates intended to maintain revenue lost from piracy of ebooks. apress above (below?) has a response detailing the legal structure of the Amazon-publisher relationship.