For non-public-domain ebooks, for sale between $2.99 and $9.99 inclusive, that are at least 20% cheaper than the cheapest new paper version, Amazon are now offering a 70% of (price less delivery charge) option for US sales.
But it's not automatic! You have to go to you bookshelf at http://dtp.amazon.com/
and manually edit the book details to specify that it's not public domain, change it to the 70% option, and agree to the new terms.
So - if you have books for sale in the Amazon Kindle store for between $2.99 and $9.99 and that meet the other criteria, get over there now and change! You'll be almost doubling your income from sales without costing your customers a penny more!