This explanation is circular. Microsoft had a legally determined monopoly, not a real actual market monopoly where no one else could participate in the market.

For instance, Apple made computers that were such sufficient substitutes for Windows computers that Microsoft chose to produce a version of one of the their core products for use on Apple computers.

30% on a $0.99 game where apple is eating the credit card costs along with hosting, making sure the store isn't overwhelmed with spam and malware and bringing millions of eager paying customers to your table hardly seems atrocious.

I refuse to believe it's anything but a cash cow for Apple.

That 30% cut got them 6 billion dollars in 2015.

Which means they made $14 billion for developers.

Wal-Mart made $130 billion in profits in 2015 on $486 billion revenue, 27%. This is how stores work.