Sean Hollister at The Verge reports on other app developers who say they were pressured by Apple to add in-app purchases to their apps, presumably so Apple could reap revenue from the transactions:
[ProtonMail] revealed to Congress that it — just like WordPress — had been forced to monetize a largely free app. That developer testified that Apple had demanded in-app purchases (IAP), even though Apple had approved its app without them two years earlier — and that when the dev dared send an email to customers notifying them of the change, Apple threatened to remove the app and blocked all updates.
“For the first two years we were in the App Store, that was fine, no issues there,” [ProtonMail’s CEO] says… “But a common practice we see … as you start getting significant uptake in uploads and downloads, they start looking at your situation more carefully, and then as any good Mafia extortion goes, they come to shake you down for some money.”
The more consistent the stories, the less Apple can claim this was all just a big misunderstanding.