It's never actually been about the 30%, it's just that that's the easiest manifestation. It's Apple's insistance to insert themselves into the relationship between developers and their users.

The fee could be next-to-free and many would still be upset if they're not able to use their own payments infrastructure. Developers are not able to offer customers refunds on IAP or discounts or credits.

Steam demonstrates that it's not about the 30%. It shows how 30% is viable in a competetive market if it's what consumers (and developers) prefer.