Setting aside whether it is justified or not, Apple is involved. Your app is heavily dependent on Apple built APIs (and hardware). Up till now, developers paid $100/year plus a value based per user royalty that was(is) part of Apple's cut of App Store purchases. Now developers will pay $100/year plus a per user royalty when the user count exceeds 1 million. If the developer stays on the App Store with a free app, there will still not be a per user charge.
Edit: I should have been specific that I was referring to the Core Tech Fee that will apply even to free apps with more than a million users. Developers will still pay a value based royalty of 10% (small devs) or 17% (large devs) for paid apps.
Edit: I should have been specific that I was referring to the Core Tech Fee that will apply even to free apps with more than a million users. Developers will still pay a value based royalty of 10% (small devs) or 17% (large devs) for paid apps.