Not an outlier and is pretty standard. When it was originally announced it was one of the best deals out there for developers writing software for phones. The WWDC audience cheered at getting 70%.
Doesn't matter. Why does the developer of the operating system get to take anything from a sale between an app developer and the owner of the actual cellphone? It is not Apples phone anymore after they sell it to a customer. Imagine if your car manufacturer wanted 30% of revenue from the shops you drive your car to.
Replace "developer of the operating system" with "curator of the ecosystem of highly affluent, paying customers" and you'll start to understand why Apple thinks they should have a cut. They see themselves as the headhunter, finding paying customers for the developer.
The WWDC audience cheers at everything.
Wasn't the market for mobile app small at the time. Almost everyone was focused on desktop and web applications. If you're looking to make millions, even preferential deals don't look like a good deal.