makes less money per book but is guaranteed to shift a large number of copies to the wholesaler - Amazon. However, the author only gets their royalties when those copies sell at retail level, not wholesale and only gets a small percetage of the final selling price. Therefore when Amazon drive the price down they are stopping the book from selling elsewhere at a higher price AND are taking money out of the pockets of the people who did the hard work in the first place - the authors.
I have heard from a number of authors who feel quite upset by Amazon's practices.