My personal comparison is between the HumbleBundle store and the HumbleBundle payments widget.

The rake on the former, where HumbleBundle brings the customer? 25%

The rake on the latter, where the game dev embeds the widget on their own website & HB handles the payments infrastructure for them? 5%

For App devs able to drive customer engagement directly themselves, Apple is effectively taking an extra ~20% of profit for themselves. Apple is treating every sale as if they were the ones delivering the customer. For $1 shovelware Apps this seems fair enough. For franchises where the Dev has an already established customer base through their own marketing efforts it seems completely egregious.