Apple doesn't have to charge 30% to also offer you convenient payment management APIs. They choose to, and they use it as a justification for their, as you say,

Apple doesn't have to charge 30% to also offer you convenient payment management APIs. They choose to, and they use it as a justification for their, as you say, "scummy business practices". You're right - you don't have a choice if you support scummy business practices with Apple. When you use an iProduct, Apple demands it. Every dime you spend on the App Store gets taxed by the richest company on Earth.