Consider the legal difference between purchasing a physical book and buying one for your Kindle. When you walk into your local Barnes & Noble to pick up a paperback of Animal Farm, the store doesn't force you to sign a contract limiting your rights. If the Barnes & Noble later realizes that it accidentally sold you a bootlegged copy, it can't compel you to give up the book—after all, it's your property. The rules are completely different online. When you buy a Kindle a book, you're implicitly agreeing to Amazon's Kindle terms of service.