Paying once for a mobile app doesn't make much sense for devs, on the desktop they'll come out with a new version a year or two later that's an upgrade or full price for the update. On mobile they can't loose their install base so are stuck supporting customers forever who aren't bringing in any more revenue. Most app developers make far more per user from ads on the free versions of the app. As much as I hate ads and subscription fees, I feel for the small app developer.