I know, I know…you’re saying "Amazon is HUGE, it makes a metric ton of money, why should they make more? They should be helping the writers out."
Understood, however Amazon is a business, and like most businesses, is out to make money. They provide the publication service (via CreateSpace) and virtual bookshelves. If we as authors use their sites, it is not unreasonable for the provider of said bookshelves to ask for their cut, even if it is only pennies on the dollar. They didn’t have to be a vendor of e-books, but they are and as a vendor they are allowed to asked for a fair cut of the profits.
Now, for those authors who have not self-published more than one book, sorry, it is my opinion and it is Amazon’s call. If you think they are taking unfair advantage, you could always stay with Smashwords and other e-vendors who would be willing to give your work away for free.