Per an article in engadget.com:
“Brick-and-mortar book stores have clearly been on the decline for a while — just look at Barnes & Noble’s rocky finances. However, there’s now some tangible evidence that the pendulum has swung in favor of internet-based sales. BookStats estimates that US publishers made more money from online orders and e-books in 2013 ($7.54 billion) than they did from old-fashioned physical retail ($7.12 billion). While the difference isn’t huge, it suggests that a large chunk of the American population is content with buying books that it hasn’t seen in person.
There is a bit of a dark cloud to this silver lining, at least for the booksellers. BookStats notes that e-book sales jumped about 10 percent to 512.7 million copies, but revenue was flat between 2012 and 2013; it may have been lower prices that triggered a surge in demand, not a renewed interest in going digital. With that said, researchers warn that their data doesn’t include books without ISBN numbers, so quite a few self-published e-books may have slipped through the cracks. Even with that wiggle room in the data, it’s evident that there’s a transition underway — you just shouldn’t expect to see the corner bookstore disappear overnight.”