> If a shopping mall was charging every store 30% of their revenue (not profit, revenue!)
In software sold on an app store, gross margin (before the app store's cut) is a lot closer to revenue than for physical goods sold in a physical store. There are no distribution costs or costs of goods borne by the vendor.
The app cost has to cover the development and maintenance costs, marketing, any overhead and expenses (like bills, electricity, those expensive Apple computers), etc.
That's the majority of your costs, not some imaginary distribution costs that you don't have because you aren't shipping a physical box. Oh and taxes too, which come out of the revenue too. And if I remember right, you are taxed on the value of the sold goods, before the 30% Apple cut (so you pay tax from that too, even though you never see the money).
In software sold on an app store, gross margin (before the app store's cut) is a lot closer to revenue than for physical goods sold in a physical store. There are no distribution costs or costs of goods borne by the vendor.