The other companies that are making money from mobile are usually front end for services that don’t monetize directly through in app purchases or give you the option of not paying through the App Store.
The first million in revenue is 15% not 30%
But also if it is just Apple, why do the same companies create apps for Android?
Let’s say in this world where there was an alternative browser engine that supported everything that you wanted, how much uptake do you think you would have for your app if someone had to download an alternate browser first?
Did I also mention that in the US at least you can link out to your own payment system?