I think the term "Kindle-books" just refers to books that can be read on a Kindle to make things easy to get for "the general public" that doesn't know about different eBook formats. I'm guessing it will be the existing ePub books going through a process similar to what the MR community Kindle-owners already use.
(Now, if Amazon just could present a nicer piece of hardware my interest to get one would be slightly raised.
I'm guessing come fall we'll see thing happening on that front as well, but that's another topic.)