Well, the difference is that with Steam EA gets the choice whether they like the "extra marketing" for that price or not. If a customer wants to buy something from EA outside of Steam, EA is permitted to sell it to them without ripping up their Steam distribution channel - which is not the case for Epic/Apple.
Yes it is. Epic is allowed to sell to every other person that's not an iOS user without ripping up their iOS distribution channel too. They chose not to do that, though, and then shot themselves in the foot on top of it to try and stick it to Apple.
Epic could sell to accounts in every other channel without having to pay a cut. In-app purchasing is just too convenient - and as a result, too lucrative.
