I'm not picking on Amazon here; it is just that I happen to own a Kindle and shop at Amazon. I do have a Kobo account, Stanza on my iPhone and I've even run into Smashwords and Audible. They all have fallen prey to the same problem. Plagiarism.
Amazon and Kindle positively promote self-publishing. There are over 30 books you can download to get you started, including Amazon's own offering, for free.
Copyright, for the printed word, isn't complex. In most countries the counting begins from the publishing of the work and last for the author's lifetime plus 50 or 70 years - at this point the work becomes freely distributable and can be used (and exploited) by anyone.
The problem arises when it is assumed that just because the author is dead or the book was published 60 years ago it must be a free-for-all.

Project Guttenburg opened up long lost books for a whole new audience; but it has also helped book-thieves profit from the hard work of others. Although these plagarised copies seem to get pulled pretty fast, I'm sure a few quick bucks have already been made at the expense and toil of others. More oversight and checks-and-balances are clearly needed in this emerging market.
You can read more about this issue at these links: