The plumber hourly wage is to be deducted from his margin. Just as Apple's costs for running the payment system and platform are deducted.

> I genuinely don't know why and how it's a number with any meaning.

It has meaning in the context of Apple arguing that their fees are that high because they have to maintain said infrastructure.

Which leads to the question "how come there is no competition to lower such high margins?", which in turns questions whether any competition in unfairly blocked by Apple.

In a totally frictionless market, profit margins are usually low. Very high margins are often a sign of a closed market where _somehow_ competition cannot emerge.