I think this system would work well for game platforms too, such as Steam. A big point of contention for Steam is, how much the platform does for advertising your game. By having two separate taxes depending on how the game was found, you can have the best of both worlds. If you do your own brand building and advertising, then those sales get a better cut, while the platform can also get their cut for the advertising they do.
This also aligns the incentives on what the platforms advertises, to some extent.
Steam already relinquishes their cut if the game is bought via a third party retailer. It costs nothing to generate or activate Steam keys outside the Steam store.
This also aligns the incentives on what the platforms advertises, to some extent.