So EA using Origin has nothing to do with it then? Last I checked if you wanted to play Battlefield for example you had to buy it off Origin. By the way there are games on Origin that use UE, therefore Epic are making money off them.
There is already one game on the Windows store that uses UE, so again Epic are making money on that, and there will also be other games coming out in 2016 that will be Windows Stor only that Epic will be making money off. It may be true that Apple don’t force you to use the App store, but nobody is going to ignore it, as they wouldn’t get sales otherwise, same goes for Google Play as well.
The point being that Epic support and make money off other people doing exactly the same thing. To be honest S or Epic shouldn’t have got involved in the discussion in the first place. Unity have supported UWP from day one and have not kicked up a fuss about it, why? Because it isn’t their place to. They support the devs to makes games and let the devs and consumer decide whether they want to use those stores or not.