Where does Apple Appstore commission for inApp purchases apply?
Yes, Apple takes a cut of the price both purchasing an app itself - and for in-app purchases. If they didn't do this, I imagine all apps would be free, requiring an in-app purchases - effectively circumventing the whole system.
This is similar to how it works on Android phones, where Google Play Store takes a similar cut of both the initial app price and additional in-app purchases.
On both the Apple App Store and the Google Play Store, the standard cut is 30% of the initial app price as well as for in-app purchases. However for subscription based in-app purchases, the cut is reduced to 15% after one year.
If the seller is a small business the fee is reduced to 15%. On the Apple Store that applies for companies selling less than $1 million worth of product on the App Store in a year. On the Google Play Store that applies for the first $1 million worth of product sold in a year.
Your question is then about shopping apps. The fees above apply to everything sold through in-app purchases. Items that you purchase by other means are not affected.
This means that for example physical goods and services, and person-to-person services (for example online fitness training, online tutoring services, medical consultations, etc.) are sold by other means, thus you're not paying Apple or Google anything in that case.
For some types of apps with digital content, Apple allows app sellers to let users access content they have purchased outside the app - for example from a PC. This is typically the so called &quot;reader apps&quot; (tv/movie streaming, magazines, newspapers, e-books, music streaming, etc).
Remember that when you purchase subscription from a vendor web site instead of through the App Store, you'll have the terms and conditions given by that web site. They might be worse than what you'll get from the App Store.