However, there is blog post at zerobeta that talks about why prices of books (and in general arts) will face pressures to decline.
Below is an excerpt:
When certain types of art such as music and literature/books become digital, the cost to produce such a work rests mostly on the artist. In addition, the Internet has made it easier to discover new artists and for artists themselves to market their work. The result is that the economics of the publishing is dead and the economics of art takes over. To the dismay of the publisher, the economics of art is much different.
Do read the entire post here. I find it thought provoking.