I think it is more about getting as much users as possible to use their store and the Windows 10 ecosystem, where they are probably planning to get most of the

I think it is more about getting as much users as possible to use their store and the Windows 10 ecosystem, where they are probably planning to get most of the money (and use part of that to fund Windows development) (Yes, Windows 8 has the store too, but I think that there are a number of difference that makes the distinction relevant)