I was quite surprised by this as well. Personally, I have never really been a fan of the epub format. Epub is really a difficult format to work with. It essentially use html code to format your book as if it is a webpage. As a result, most doc to epub converters do a rather poor job at making good quality conversions. The process to build an epub book is rather laborious compared to the traditional document format. I did not realize that so many people actually fancied this format over kindle.
