I think Apple is right on the line. But I don't see a good argument as to what their doing is being anti-competitive. ~2 million apps are on the app store. Charging a fee for giving developers a huge market that spends money is not exactly unfair. And the rules of engagement are generally applied equally to everyone - the exceptions are noted by the guidelines.
What would make it fair? Lowering the fee? If that were the case, then the problem isn't anti-competitive behavior. If it's the rules, what would fair rules look like that don't harm the end user or the product?
What actual harm is Apple inflicting on the market by their behavior? Developers make less money? That isn't good enough.