Retailers don't get 30%. Not even close. Try 0.5% or something like that. As for MS, their cut on the MS app store is 5%. 30% is just really really steep, and I think consumers would win if that got reduced.
The end user got a nice discount and Epic still pockets more because interchange fees are ~2.5% and not 30%.
The Epic Games Store had a similar strategy, cut the fee for devs and incentivize end users to move onto their platform (weekly free games). They still make a boatload of money even though it's not as much as Valve's money printer.
In general I see this as a great thing for devs (indie in particular) if it triggers more competition to bring platform fees down across the board.
Epic isn't being overtly greedy with end users (yet)