Isn't part of the problem how US anti-monopoly law is worded requiring proof of "consumer harm" which is normally measured in increased costs? In the case of Apple's monopoly, its not clear how you would measure that let alone prove it to a court.
This is more a matter of interpretation, policy and practice rather than statute and these things can change over time. The interpretation you're describing was itself an innovation at one time.
> I am curious though, why is the iOS version €4.99 but the Android version is free ? I've seen this a lot actually and have always wondered, I figured it might just be Apple's annual developer license fee but not sure.
Apple users are being forced to pay more for equivalent software because of Apple's tax.