Google's right to order its search results as it sees fit.
You mean, to present them from least relevant to totally irrelevant?
The App Store replaces your shopping cart and shipping desk, not your sales and marketing department.
It also replaces 30% with nothingness, since, as you said, you still need your sales and marketing departments.
I've yet to read any developers say that the MAS replaced their departments, thereby making the "Apple MAS Tax" of any real value.