[dwaite]

I've long believes that the requirement to use in-app purchasing was to make such revenue sharing easier to audit - if you can only use Apple's payment system to do certain things (or else your app isn't approved), then Apple doesn't have to worry about things like audits.

Since various countries have regulated the ability to do third party payments from apps, Apple has since added API to launch said payments, to help generate statistics on use so that they can then demand third party auditing that the commissions are still being properly paid.

In the US there was a court decision that they couldn't meter or charge commission, which may very well be walked back and will lead to lots of fun future articles.