IF there weren't App Stores or anything, it would be possible to download applications from websites.

So basically you would distribute the same way as in PC. You buy the install files in physical/digital form and install it. Then enter cd-key or something.

And of course somebody would come and make some kind of store to make the purchasing easier just like on PC. (for example Steam)

And yeah. Its ridiculous when Apple/Google take shares of the profits, comparing to what UE4 for example takes.