Apple has been asserting control of its App Store rules by asking app developer to remove the "purchase" buttons for third-party stores in certain apps. The most obvious ones impacted by this have been the Google Books and Kindle apps.
Last night, I discovered a bit of clever marketing on Amazon's part in response to this change.
When someone launches the Amazon.com Kindle Books page, Amazon presents a popup prompt instructing visitors on how to install a Home Screen bookmark on their Kindle iPad, so they're only one-click away from their Kindle books.
I'd love to know how effective this may be for Amazon over time. Either way, it's a clever bit of marketing.