Apple has restricted the ability of an app to point this out so it's not as well known as it should be. Subscriptions are the easiest to compare because you can order the exact same thing two ways on iOS (in app or web) and there it's easy to see just look at Netflix or YouTube or Spotify for obvious examples of apps avoiding the cost or costing more if you pay the Apple tax.
It's a bit silly this needs to be defended by example though, where else do people think the 30% cut on stuff subscription is coming from? Certainly not a 30% margin cut or 30% for payment processing, it's ~27% Apple tax apparently.
You are thinking from the point of recouping the costs, while in reality it works on a simpler premise: profitability.
Suppose you have your Android app. You are thinking about porting that to iOS. So, for you the calculation will go like this: will selling that on App Store be worth it after paying Apple's fee and cost of porting? If the answer is yes, then you proceed to expand your app's market share. You may as well price your app differently, if you think that will sell more.
You've oversimplified on the assumption there is only a single transaction rate (30%). In the real world there is not (even on iOS, though Apple does make it difficult and force it to be hidden), hence why the real world examples given above did not follow your theory the 30% is built into the initial optimal price setting. It ended more like 3%, i.e. the average transaction rate, for anyone not using IAP and as close to +30% that could be reached using typical $0.99 or $0.49 price increments for anyone using IAP (or just cancelling IAP).
This is what the above examples are actually doing, not a theory of what I think it makes sense for them to do.
In the Apple utopia where everyone would always use their payment method your simplified answer would be more correct and the Apple tax would be somewhere between >0% and <infinity% (though usually marginally less 30%) as well as a unique value per app. It would never be <0 though it would be possible (and almost expected) for the app price difference between platforms to be greater than the Apple tax alone. This method of course is god awfully impossible to actually compare as it's theoretical values of multiple what-if's, hence why I went the "more complicated" route of just explaining the Apple tax has to eventually hit the consumer on some level from a recoup perspective.
I noticed that in games here in Brazil, in Hearthstone, a card game from Activision Blizzard a 40 cards pack cost 279,90 BRL ($52) in the iOS app, if you buy in the PC app it'll cost 99 BRL ($18), almost 200% increase, crazy.
Do you have examples of software that costs more on iOS than elsewhere?