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.
So I will use [x] to find a game in [y] and then [z] it to play.
Where: x = {Chrome|Firefox|Steam}, y = {some-sort-of-web-app-store|Steam store}, z = {cache|install}.
I guess the success will depend on how easy and rich x-y-z experiences are, but you will still have to register, pay and download.