A lot of developers are now complaining that they're getting burned by what is a reasonably obvious profit motive from Apple. They're not offering an app store because they're good guys. They're offering an app store to make money.
They take 30% of purchases. It only makes sense to take 30% of in-app purchases and related subscription services as well. Did anyone honestly believe that apple would fall for the ebay $0.90 purchase with $90 shipping fee-dodging trick? Letting subs through just opens the door for people to ship free apps with subscription "unlocks", thus cutting out Apple.
The simple fact is that Apple owns the mountain, and if you want to mine their gold you can expect to pay their taxes.
Of course the simple solution is to just build a web app (as these guys have done). Why restrict yourself to Apple's yard and Apple's rules when you can target every device without rules, without restrictions and without a 30% tax? The sooner ever developer realizes this the better off we'll all be.