Not true at all, you can buy the
amazon books which usually have the best price, but if you want to buy them somewhere else (ibooks or even kobostore) or
get them for free on project gutenberg or any other source all you have to do is to load them on an app called calibre (available for mac, linux and windows) which will automatically convert the
books into the more appropriate format and send them by email to
amazon cloud which will make them appear almost imediatly in your kindle.
Doris Booth is the author of UNLOCKING THE SECRETS OF E-BOOK PUBLISHING,
GET YOUR
BOOKS INTO EFFECTIVE SALES CHANNELS (WITH OR WITHOUT
AMAZON), available in both e-book and print formats.