From the Amazon press release:
Amazon.com … today announced that RosettaBooks has released four books by bestselling author and Congressman Ron Paul exclusively in the Kindle Store (www.amazon.com/kindlestore). The books–“A Foreign Policy of Freedom,” “Pillars of Prosperity,” “The Case for Gold” and “Abortion and Liberty”–are available as e-books for the first time, and they will be exclusive to the Kindle Store for one year. Customers can download these books from the Kindle Store for $9.99, and can read them on their Kindle, Kindle DX, iPhone, iPod touch, BlackBerry, PC, Mac, iPad and soon, Android phones.
Not entirely accurate. The Mises Institute has offered PDFs of Pillars of Prosperity and The Case for Gold for a while now.
http://mises.org/books/prosperity.pdf
http://mises.org/books/caseforgold.pdf
Abortion and Liberty is also available as a PDF thanks to a loyal fan who says he got permission from Paul to post it (http://www.ronpaulforums.com/showthread.php?t=66303). So it looks like A Foreign Policy of Freedom is the only one you can’t get for free. Of course many people don’t like using or converting PDFs, so maybe that’s reason enough for people to buy the e-books anyway.