You need to reexamine the Amazon customer comments that this article is based on. Nobody is saying that ebooks are less useful therefore they should cost less. If that were the case people would simply purchase the hardback copy and be done with it. This is simply outrage over the "fairness" of charging more for something that is cheaper to produce.

Here's my evidence:

Sunk cost fallacy: http://cl.ly/1V0Y2L3W2Y0l3A3S3F28 Fairness in cost fallacy: http://cl.ly/0i3u0V183e0g273l421e, http://cl.ly/3s1Z3l3w06291g0N0W15

Who is saying that the Kindle version is worse?