That one Apple is still allowed to collect fees on (which I'd love to see the provided justification for!).
Per the article: "Apple can no longer collect a 27 percent commission on purchases made outside of apps or restrict how developers can direct users to alternate payment options"
This now allows folks to direct users to alternate methods. Before this the Kindle app would just say something along the lines of "you can't get a book here, please use the website".
I'd have expected it to actually make the purchase using my card on file with my Amazon account, just like the physical Kindle does.