Am in the 20%
The other 80% obviously haven't looked at the retail business. Nor at the Nokia app store from a while back which was at 40% for Nokia IIRC. Ditto Handango.
The real value of this model is that it allows developers to concentrate on... developing and, maybe, marketing. Rather than billing. And it avoids customers having to sign up and enter credit card info on tons of different payment hosting websites of unknown hacker-proof-ness.
For all its technical backwardness that is one thing the French 3615 Minitel Teletext system got right in the 90s. Massive numbers of online services were made available and some made a ton of money because the customers just paid up through their regular phone bill.
Anyways....
I think the next logical step would be a company that hosted for-pay web services. For example, you could write up a bank account number validation service in SOAP/REST and charge for it. The hosting company would host many web services, using a generic sign up procedure and would take a cut of each transaction's charge. The customers could shop around using several back account validation services (or tide calculator or naughty SOAP messages) without signing up at multiple sites.
I pitched this idea at some colleagues and they of course thought a 30% cut was too much and they would rather spend time writing their own billing system to support the validation service.
p.s. a large volume discount (say 20% rather than 30% past a certain number of sales) would be nice, your Jobs-iness.