I thought it was kind of neat to that a library I'd written was one of the 45 included. I was kind of curious to see what they'd changed, but it ended up being a little boring:

https://gist.github.com/1289293

It's a library for reading / writing audio meta data (tags) and they basically just removed support for several formats. What's perhaps more interesting is what they didn't remove: I don't have a Kindle, but from the code this would seem to imply that it supports Ogg Vorbis and FLAC in some capacity.

Also noted that they're using a version from early 2008, even though there have been 5 more recent releases since.

Edit: I also went back and grabbed the very first Kindle release, which contained only 22 packages (TagLib still being one of them), and there they used an even older version (meaning they do at least sometimes grab newer versions of the libs).