Just to clarify for any others who misread the title, this is comparing paperbacks to Kindle edition, not all paper books. The numbers imply Kindle sales are about 85% of hardcovers and paperbacks combined.

Also, since Amazon sells 100% of the Kindle books its readers buy, but only some of the physical books its readers buy, I think this most interesting part of this release is what it says about how great a business move the Kindle was for Amazon. Every time a customer switches to the Kindle they instantly gain a lot of sales that used to happen at various physical bookstores. And that's before even considering that people who walk around with a bookstore 1 foot from them will buy more books, too.