Its funny, if you don't care.
Apple started the 30% thing, and whinging aside, it was a smaller cut than the alternatives. That doesn't make it great that the new pimp in town takes a smaller cut than the establishment. Independently selling software takes some effort - you need to set up services for delivery, validation, payment and communication. For a software outfit, this overhead is easily more than 30%. This model is actually a bargain for the lower volume publisher.
For the higher volume publisher, they need to shadow some of these services regardless of the App store. For example android, amazon and even blackberry variants. Ok, joking about the latter. The value of the App store is less to them because of this.
So, naturally, the low-volume publisher, which relies on more services of the app store, should be given a discount, whereas the high-volume publisher who only patronizes the app-store because of (mono/duo/trio)-poly laws being largely useless gets to pay full whack for a useless service.
Nice work you don't be evil dudes.