Many kindle books are priced at ridiculous levels, if I am going to pay the same as, or above a hard-copy price I want to receive both a digital and a hard-copy version!
Quite frankly, at the end of the day, if I'm to have a digital-only version (which is, really just text!), I want the price to be at most two-thirds(or half!!) that of a hard-copy (especially on titles that you could probably get a hard-copy for next to nothing second-hand)!!!