Originally Posted by wallcraft
TOPAZ ebooks are created for the Kindle by Amazon on behalf of the publisher. This means that is usually isn't available in any other format at other ebooks sites. I have seen a few TOPAZ titles being replaced by MOBI later on, but if you buy the TOPAZ you don't get the MOBI to replace it (the MOBI is a different ebook in the Kindle catalogue).
Unfortunately that is not true. I bought "Avengers of the New World", a book about the revolution in Haiti. It is also available elsewhere, but on Amazon it it is in Topaz. It was 4 bucks less than on Sony, so I threw caution into the wind and didn't check the sample first.