Separating The Novel From The Book

How much should you pay if you wanted to get one book in several formats, say paperback, hardback, e-book e.g. Kindle and talking book? You may ask: why you'd want the same thing in many formats, but for some books I do. 

Currently each purchase is seen as a completely isolated transaction, but why should you (or me) pay for the artistic content 4 times over?

I can understand needing to pay for printing of the paper copies or audio production of the mp3 and even marketing of the various formats, but why do I need to pay the artist full whack for their content on each separate media.  I want the story, but once I have it, why should I pay for it again in a different format?

If the principle of separating purchase of the story from purchase of the media were accepted, there would be significant problems in putting it into practice.  Probably the biggest of these would be to stop  individuals providing copies of books (in a second or third format) to friends at minimal cost.

I'd be interested in your views on the principle outlined.  We can look at the difficult practice later :-)