Amazon don't have to pay 30% for every transaction I make through the Amazon app on my iPhone. Same with eBay. Yes, I know Apple class these as different categories, but when push comes to shove what's the real difference here?
Epic are providing electronic assets that they have paid in-house artists to create and want to distribute in exchange for their in-game currency (V-Bucks). Why should Apple cream 30% off the top of that revenue?
Other than the electronic distribution, Apple has no fixed or variable costs relating to these in-game assets.
I fully agree Apple should take a cut of Fortnite being a reviewed, and therefore trusted, app on their store. I find it hard to justify the ongoing 30% cut of additional assets that bear no discernable cost.