The point is that unlike, say, Netflix, I am not paying anybody to serve me licensed content. I am donating (extremely selectively in my case) to specific publishers. It's hard for me to see how Apple needs to be involved here.
I should add that I never used Readability and used Instapaper extremely rarely prior to this scheme. My only interest here is that this is the first content micro-donation scheme that I have seen that allows me to pay for content I like. I don't see where Apple fits into this, morally.
Let me ask this question: if there was a free Red Cross app that allowed you to make donations, should Apple get 30% of that?
Let me answer your question with a question: Does Visa take a percentage of donations made to the Red Cross using a Visa credit card?
If Readability wants make an iPhone app, and keep giving $7 for very $3 they make, they'll have to make their in-app purchase price $14.99. Also they can't charge less anywhere else.
IAP price = regular price / 0.7 then rounded up to the nearest integer (less a penny).