I think it's the price for eBooks. A good example is Fear and Loathing in Las Vegas:
Kindle - $15
Paperback (new) - $10
Paperback (used) - $6
Paperback (library) - Free
The Kindle version is a significant premium and I don't think there is a matching convenience factor. It's unfortunate that is the case because I'm sure it'd be a lot more eco-friendly and efficient to distribute ebooks.