I’m not sure what you’re referring to here. Google are the file distributor for content from their store.
These rules aren’t for linking out from the store to a third party site, but rather for installing an app from the store and then linking out to a third party payment.
Choosing a price based off the cost is just one pricing strategy. Another is to do it based off the value it offers a customer along with the price competitors are charging.
The four dollars is for providing the platform that the user used to navigate to the link and download the zip file.
That's a fun bit of argument from the owners of Chrome.