We're here to support authors and we encourage you to buy their books wherever! But here are three reasons to buy their book on Leanpub:
Leanpub offers content creators higher royalty rates than Apple or Amazon do. This is way more than they would get with a traditional publisher, and even more than they get when selling on Amazon or Apple's bookstores. We show you how much money the author gets right on the purchase page; how many other publishers do that?
If the book is being published in-progress, you can give the author feedback before the book is done.
With in-progress publishing, you can get early access to the author's latest thinking, without having to wait for the full conventional publishing cycle to end. Since you'll receive free updates until the book is completed, you'll always be up to date.