It doesn't even need to be the same or lower than competition. Since there are so many apps already integrated (and even in future their API might be easier or more likely to be used by app users) and nobody wants to go through the friction of adding new ones they can still be slightly more expensive and retain majority of the market share.
But if they won't then I guess you will know it never really was about protecting the user or whatever, just a cash grab from walled garden.
I can't imagine it would be difficult for Apple to implement this for their stores. Maybe someone who works in this field can chime in..
If the choice is left to developers, each developer will choose what suits him best.
Isn't Apple just forcing everyone to use what suits them best?