Yeah, you're right that it's not a perfect analogy, but I think mine is closer to reality than OP's... There are plenty of apps (stores, in the analogy) out there that are actually designed to work on many platforms (with many cars, in the analogy), but still have to pay the store %.

The broader point is that just saying "oh, it's like X, therefore we should treat it like X!" just isn't enough for app stores. There is no perfect analogue. Apple and Google call them "stores" because they really want them to be thought of that way, but there are important features of phyiscal stores that the app stores lack, and important features of app stores that physical stores lack.

How we, as a nation and a society, decide to treat app stores for purposes of consumer protection laws is up to us... so let's be careful just blindly trusting the way these companies want us to think about them.