In a nutshell, publishers set Kindle prices and Amazon has little control over them. The publisher's Kindle price is less than the publisher's hardcover price (about eighteen bucks). However, Amazon can and does discount the hardcover price, so it comes out cheaper. Really, this is an indication of how much publishers are gouging customers - Amazon can sell the book at the discounted price and still make a profit, so imagine how much money the publisher gets when you pay full price.
They can't discount the ebook because publishers forced Amazon into an agreement that lets publishers, not Amazon, set the ebook price (that's why below the price it says "This price was set by the publisher").
Check out this article on The New York Times from when the agency agreement happened: http://nyti.ms/H75RZj and this more recent one from The Guardian: http://gu.com/p/34ay7
This is a ridiculous statement, "Imagine how much money the publisher gets when you pay full price?" To begin, the publisher has published endless numbers of books that didn't make any money and when they published this book they didn't know if it would make money. Maybe John Greene would have suddenly become a version of A Million Little Pieces, the Oprah book pick author who turned out to be not so honest in his writings, and then the publisher would have had to pull the book and eat all the costs of the following: multiple editors...editors for acquiring the book and negotiating, and then after that there are editors for storyline and editors for punctuation and grammar and then there are teams of editors who come together and try to determine how the book will place in the book market. Of course, there has to be a book designer for the exterior and this is rarely the book designer for the interior so another editor for the interior. Then there is the sales team who has to go out and represent this book as well as the other 100s of books that the publishing company needs to be successful to keep the lights on, pay the office staff, and pay for all those nice computer upgrades, pens and pencils and paper or whatever. Then there is advertising to pay for and the public relations people at the publishing house who do the very difficult job of trying to garner attention for this book as well as the others that are on the publication list for that season. Now we haven't even started talking about the real estate (rent) for the publishing house and then there is the cost of taking authors to lunch or sending them a bouquet of roses and/or nurturing them along while the "creative" spark ebbs and flows (and that emotional toll on the editors is another story altogether. So ya, whine and complain about the cost of your book and its price but remember: you don't want amazon to be the only person in the room setting prices and that also degradation of prices tends to diminish "perceived value."
If I was the author, I'd have it built into my contract that Amazon couldn't have any of my books for sale for less than a "stated" amount. After all, I spend several years writing and rewriting this book, and unlike Stephen King who seems to be able to pump out best sellers like a chicken laying eggs, many authors may only have one or two really successful books. So pony up your bucks, skip a ridiculously exorbitant Starbucks, and know that you can come back and share the words of John Green with your brain again and again because you are now the proud owner of a book, written by a real author instead of one of the cra$$y instant books that is just recycled and rewritten garbage from someone who will put up anything (most often rewritten through a rewriting program that cost ten bucks) on Amazon clogging the place with junk. Lastly, so buy the book and while your at it buy one and send it to someone else because somewhere in the world of vampires, books of degradation (think shades of gray), and books that purport to get everyone rich in five minutes, a book about deep love in the face of unbearable hardship is a great thing. Thanks to John Green.