Sure, putting files on a CDN is very cheap. But, point of sales is a massive pain in the ass. Updates are a massive pain in the ass, notifying users of updates and security patches, not to mention marketing. These things are such a huge pain that I can see why a platform would charge more than pennies for them.
Facing building out exactly this stuff myself using Stripe, a traditional website, building in licensing keys, etc etc. If something like the app store were multi-platform and had a bit more support around offline licensing and things like upgrade pricing, then honestly I would not immediately discount it even at 30% cut. Especially if I got some marketing out of it too.
You can argue wether 30% is the right number, but what the app store provides is definitely not "basically nothing".
Facing building out exactly this stuff myself using Stripe, a traditional website, building in licensing keys, etc etc. If something like the app store were multi-platform and had a bit more support around offline licensing and things like upgrade pricing, then honestly I would not immediately discount it even at 30% cut. Especially if I got some marketing out of it too.
You can argue wether 30% is the right number, but what the app store provides is definitely not "basically nothing".