What changed between versions of the Amazon Appstore?
After you posted this I got curious too but I couldn't find a change log.  I emailed Amazon support and asked what changed and where I could find a release log and here's what they said:


  Unfortunately we do not have a change
  log detailing the changes made between
  versions of the Amazon Appstore app.
  
  I will forward your feedback on to the
  Appstore team who will take them into
  consideration. Customer feedback like
  yours is what allows us to continue to
  improve and provide a quality product
  and experience.
  
  If you have any other feedback please
  let us know via email or at
  1-866-749-7771
  
  Thanks for contacting Amazon.


This is actually the most direct answer I've gotten.  I've emailed them a couple other questions and got boilerplate responses that looked like they were for different questions.