This is good for smaller developers, but it doesn't really seem to solve the actual problem? All the people who are willing to go to war with Apple and have teeth are making way more than that…
In a warped sort of way, I can think it would be useful to have it the other way around. A small developer doesn't have the resources to build and maintain their own billing system, promotion, etc, so 30% is probably reasonable. A larger developer, however, can, or already has those things, so to being forced to pay 30% is not reasonable. That's before we consider margins rather than takings.