No, Amazon have locked the Kindle down to ensure it only uses their propriterry format, ensuing Kindle owners only have one port of call when it comes to buying content.
it's like a car that will only accept petrol from a particular garage.
Sony, Kobo, B&N, Apple and basically everyone else in the world are using the EPUB format.
For content, you can use Kobo or Google Books, or perhaps Sony might get their offering launched sometime in our, or our childrens lifetime.