I think you're forgetting the +$3.99 shipping on used books at Amazon. I mostly don't buy used paperbacks if they're still in print, unless I can find them in batches on ebay, because the shipping tends to raise the price to close to new. That's an interesting point, though; as far as I know there is no way to resell a Kindle book. I generally keep books anyhow, unless they're just bad, but people who sell most of their books would also not be well-served by the Kindle.