See the link below for more e-book market dynamics
One reason Kindle book sales have held their own is that owners of iPads and other mobile reading devices buy Kindle books, which they can read on computers, iPhones, iPads, BlackBerrys and Android phones. But, except for the free uncopyrighted books, Kindle owners must buy or download content via Amazon. “Every time they sell a Kindle, they lock up a customer,” Mr. Shatzkin said.
Some industry analysts say that many people do not consider the iPad to be a reading device the way the Kindle is, and see a need to own both. Amazon’s latest sales figures are “clearly an indication that the iPad is complementary to the Kindle, not a replacement,” said Youssef H. Squali, managing director at Jefferies & Company in charge of Internet and new media research.