I don't know, in theory that's why they get 30%, to figure that out.
> Apple never claimed promotion they claimed access.
From their website [0]: "the all-new Mac App Store beautifully showcases your apps and makes them even easier to find."
> Do physical retail stores actively promote your SKU over the thousands of other products?
They most certainly do. If you've ever worked in retail you'd be familiar with the daily restocking sheet, where we had to move certain products to the eye level shelf and other ones down.
Look at your supermarket. The end caps change all the time. This is a combination of those brands paying for those placements and the store putting high margin popular items up front.
But the point is that stores accept different payments from different vendors for different levels of promotion.