Today an estimated 75 percent of online book purchases in the United States are made through Amazon, and its overall market share in book sales is astonishingly high. Some publishers make more than half of their sales through Amazon. So when Bezos rang the death knell for the physical book, people paid attention. Even before the Kindle, Amazon wielded enormous influence in the industry. Now it is positioned to control the e-book market and thereby the future of the publishing industry.
Want to read more, here's the link (thanks Joni for always sending such interesting items!).