Amazon charges 15% for physical media, including software [1]. Since Apple is not shipping physical media, it seems something less than 15% would be more reasonable.
1. https://sellercentral.amazon.com/help/hub/reference/external...
1. https://sellercentral.amazon.com/help/hub/reference/external...
The link you provided is only for "Referral fee", not whatever fee charges to fulfill the order (ie. warehousing and shipping), which is separate: https://sellercentral.amazon.com/help/hub/reference/external...