[jon_hendry]

So if my broker has an app, and I use it to buy a million shares of a company in my account, Apple should get 30% of the transaction?

For what, providing networking functionality?

[halostatue]

No. For many reasons, but one in particular:

Your broker cannot offer an app with IAP that does purchases of goods or services that cannot be used in the app itself. (iOS Developer Agreement, schedule 2:1.1)

This is all about IAP. If you aren't allowed to offer IAP for your particular item, these rules don't apply. If, however, you could theoretically use IAP for your content, you cannot offer such a service solely through external purchases.