If you have an issue with Steam's cut you can simply sell on one of its competitors. Many companies do.
I'd say that's a fairly big difference. Whether that's enough to be considered a different market, I do not know, that's for regulators to say.
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Walled gardens have existed for 4 decades. Nintendo, Microsoft and Sony all had/have them. “What Apple is doing is not much different … they created a platform.”
“The 30% of what you complain seems to be the industry rate, right? Steam charges 30%. Microsoft: 30% … If you go to consoles: PlayStation, Xbox Nintendo all charged 30%. Physical stores: GameStop, Amazon, Best Buy, Walmart all charge 30%. Apple and Google charged 30%. It’s all 30%, and you just want to gloss over it. You don’t want to address it,” Judge Gonzalez Rogers says
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[1] Quoted from https://edition.cnn.com/2020/09/28/tech/apple-fortnite-epic-...