The publishers of Harry Potter simply refused to stock the latest ebook with Amazon.
When Pottermore launched their ebook store at the end of March, the publishing industry stood still and watched in amazement. Pottermore did something that no one had dared trying before: they forced Amazon to send customers to their site to buy their ebooks.
Some publishers had been thinking about it in the past but concerns about the consequences this could have created to their revenues in case Amazon disapproved and retaliated proved too big to overcome. Controlling the purchasing stage of the user journey is extremely valuable not from a financial but from a strategic point of view: who sells the ebook owns the relationship with the customer.
Pottermore showed that if you are big enough you can actually do it. This precedent is extremely important as it has shown to publishers that if they were to go down this route they could potentially succeed in shifting the power form the retailers back to them.
This is from Futurebook.net and you can read the rest of the story here