E.g. you sell the in-app "iPhone exclusive" version for $x and the out-of-app "everything except iPhone" version for ($x * 0.7) and then provide a "works on iPhone for no extra cost" special offer.
If Spotify was called Spatify on the app store, operated by a company that's owned by Spotify, their product wouldn't have to match the pricing of Spotify products on non-apple platforms... and perhaps 'Spatify' could announce a deal that allows Spotify customers to use their product for free.
Then it just comes down to whether Apple follow the rules by the letter, or apply common sense and tell Spotify not to take the piss.
I suspect if any company did this they would put a lot more research and thought into it than I have for my two quick HN comments - I'm really just wondering what, if somebody took this approach, Apple's response would be.
They're not legalistic, they're moralistic.
But the market is. No company is going to charge 30% extra on other platforms - competition would eat them there. So at worst there will be a split into Apple-only and No-Apple companies, at least for commodity repackaged content.