Third party payments are a great example. Say I sell an app that lets you pay for movie rentals at a RedBox kiosk that does so by letting you select and purchase on your phone/tablet and sending the right instructions to the RedBox servers so that your rental is prepaid when you arrive at the box.
Do I owe 30% of what was paid to RedBox even if I as the app developer am not RedBox?
Then let's talk declining balance accounts, a subcategory of the above. For example, your lunch money account at college. Your mom might put $500 on that account at the beginning of the school year from her home computer. You then use your phone in the food areas on campus to pay from your lunch account.
Is this considered a virtual currency and therefore Apple gets 30% every time you pay for lunch? It definitely is based on how I read Apple's agreement.
Since Redbox is NOT actually providing content to your device, there wouldn't be a problem there.
Still, the 3rd party seller argument is a mystery in cases where these rules would normally apply.