Only 2 of Amazon's 20 all-time best-selling were published before the Kindle was launched

"The importance of e-books to Amazon can be seen in a few different ways. Of Amazon’s 20 all-time bestsellers (in any format), only two were originally released prior to Kindle’s 2007 launch. (Another observation from the top-20 list is that all the titles are fiction except StengthsFinder 2.0). Second, in 2011, Amazon customers bought more e-books than print books for the first time, a trend that continues today. Despite an industry-wide slowdown in e-book sales, Grandinetti said Amazon continues to see a transition from print to digital, adding that “our Kindle business is growing.”"
Source:  Publishers' Weekly, 4th September 2015