There are all sorts of reasons. But the simplest one is this: people will pay it. Just because one product costs less than another to make doesn't mean that it must sell for less than the other.
As long as WE pay the exorbitant prices they will continue to sell them that way. GO TO ONE OF THE NOT SO POPULAR GUYS. Hit them in the pocketbook, it is the only thing they will understand!
I've found the eBooks I buy vary greatly in price. Some are more than paperbacks, others are less. For what its worth, my most recent purchase "The Girl With The Dragon Tattoo" is currently $5.21 as an eBook and $10.76 in paperback.
The companies shouldn't have to tell us diddly squat about how much it actually costs to provide us with a product. If we don't like the overall price.. we shouldn't pay it. Ask any asian lady (that came from an asian town like my girlfriends mom did*) and you'll find that the best way to get a lower price is to make sure that the seller KNOWS you will walk away if the price isn't good enough.
I think the price should stick with the Paper prices. New release, in hardcover, is X, so ebook is X. Months later, Mass Market Paperback hits the shelf and the price is Z, now ebook is Z.
My only gripe is if the Mass Market paperback is less then the ebook. That's when I sit back and don't buy it till the price drops.
We got the power, people.