This article http://online.wsj.com/article/SB1000...LEFTTopStories
makes the point that ebooks seem to only rule in "disposable" fiction - and that pbooks are much stronger elsewhere.
Readers of weightier fare, including literary fiction and narrative nonfiction, have been less inclined to go digital. They seem to prefer the heft and durability, the tactile pleasures, of what we still call "real books"—the kind you can set on a shelf.
E-books, in other words, may turn out to be just another format—an even lighter-weight, more disposable paperback. That would fit with the discovery that once people start buying digital books, they don't necessarily stop buying printed ones. In fact, according to Pew, nearly 90% of e-book readers continue to read physical volumes. The two forms seem to serve different purposes.
Considering that most ebooks are locked into a platform, I could see this being true. Personally I prefer not to buy pbooks any more, much prefer reading on my Nook Color.