Valuing a book by it's physical properties is a practice that's gone on for far too long. Lots of technical books are full of "padding" and duplication because no-one will buy a 50 page book which concisely provides the useful information for $10-$20. It waste a huge amount of time both of the author and the readers.
1. Modern Algebra by John R. Durbin
2. Introduction to the Theory of Computation by Michael Sipser
3. Machine Learning - An Algorithmic Perspective by Stephen Marsland (not quite on the same level as the above two, but still pretty solid)
I think Tanenbaum's Operating System and Appel's Compilers books both go in this category too, they're big but not compared to their subject matter. But, I've seen enough people disappointed in both to think this is more my personal opinion at play.
I think if we are talking about entertainment books (novels and such), there simply is too much competition. At the end of the day, a lot of those entertainment books could be exchanged for another entertainment book. I suppose for similar reasons cinema tickets tend to not vary too much with the content of the movie?
A few years ago Stelios of EasyJet fame tried to start a cinema chain which offered dynamic pricing, Warner Bros, Disney, and 20th Century Fox all refused to licence any of their movies to him which more or less killed his business.
Until you find those authors you adore to that degree, however, yes books are totally interchangeable after a certain quality threshold is passed.
On the flip side, the convenience of ebooks helps to defray some of these obvious cons.
It doesn't when an ebook is priced higher than paper editions with the same content. I do agree on the padding, though.