According to a New York Times article from September 2015, digital books account for only 20% of overall books sales, representing a decrease of 10% in the first 5 months of 2015 (NY Times September 22, 2015, The Plot Twist: E-Book Sales Slip, and Print Is Far From Dead). Thus, most readers still read hard copies. In order to capture the most sales, then, it makes sense to publish both hard copies and e-books.
