The legal factor mentioned in the OP article is big when the author is hard to locate or deceased. But I think the OP article underestimates the work involved in proofreading a scanned book.
Here's a bestselling no-eBook-available 1994 book with a living, New York City-residing, author who still has (allowing for mergers) the same publisher today:
http://www.amazon.com/Power-Broker-R...s=robert+moses
Author Robert Caro's newer books are eBooks, but his first is not. While there could be some complicated explanation in this case, I think the most likely reason for much I want to read being paper-only is that correcting misscans is expensive.