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EU fines Apple $568m for deterring third-party payment methods on App Store
(www.gamesindustry.biz)
This is a most excellent place for technology news and articles.
Curation and encouraging PC ports when the store was relatively new != exclusives.
Steam Greenlight was a program where independent games without a publisher could release games on Steam, but it was absolutely exclusive. They couldn't sell their game elsewhere.
Literally the first game released on the program was a free Total Conversion mod that you could download anywhere else for free, but if you wanted to get it installed through Steam, you paid them for the privilege.
The dev made money from at least the iOS, Android and Steam Greenlight versions. They also offered it for free.
https://www.giantbomb.com/articles/mcpixel-embraced-piracy-lived-to-tell-the-tale/1100-4366/