But crucially you will be able to buy on the app using x,y,z, and continue to play the app using a,b,c from different hardware/software vendors, unlike the situation today with say a game bought on a mac.

That's the advantage of the web over native APIs, and why I think its ethos will eventually win out - it is better for developers and users, but not for the corporations who would like to sit between the two as intermediaries.