So if I buy one on my PC a while back, then go to my Kindle app on the iOS device and then Amazon has to hide it because it wasn't bought there?
This is actually Apple, which I own many products, being anti-competitive on allowing other bookstores at all besides iBooks.
This will force possibly the market to go more PDF and away from DRM, maybe a good direction in the end. Amazon should switch to PDFs. Then you can load those up in iBooks.
What makes iOS purchases different are two things:
1. Apple has oversight of content being sold (helps avoid malicious software in many cases, and age appropriate content).
2. Ease of use - one password to buy stuff, not multiple accounts everywhere.
That's what you get as a customer. As a developer, you don't have to deal with the payment processing and other consumer financial issues, to a great degree, and they provide marketing.
There's nothing to stop an end-run around any of this - you can still make totally open web apps, content in PDF and ePub formats, etc.
You just can't provide the identical guarantees Apple provides with the oversight of their store (which necessitate a locked down device and limitations on what 3rd parties can do outside of their system).
(edit: formatting fix)
I thought the whole point of this outrage was that Apple was trying to stop the end-run. This step isn't a complete blockage, but they're certainly trying to make it harder for customers to get content from outside and easier to get it through Apple's paywall.
Apple has little value add here and as their store grows, the long tail and new business models suffer due to there being only one store. AppleVAT is a good term for what they do. Their strategy is almost guaranteed to make the company less innovative.
So you mean now Apple is going to have to approve eBooks before they appear on the iOS Kindle app? Oh boy.