Microsoft: Pay me $250 instead

If this article is accurate, Microsoft is paying Nokia almost $250 for every Windows phone that Nokia ships.  The payback, ostensibly, is twofold:

1. Wide enough adoption that Microsoft becomes a player in mobile
2. People, through usage, will stick to Microsoft services, and become long term customers.

I wonder if Microsoft could achieve both aims through a software-only play?  I imagine buying my new Android phone, and then installing "Windows Phone 8", the App, for which Microsoft will pay me $20/month for every month that I am an active user.  They can do that for 12 months for the same amount that they are paying to Nokia, so they have a full year to make me a believer in Microsoft solutions.

Of course, Google may react and try to shut down, or limit, such a practice.....but operators might endorse it.  More Microsoft services, more data usage.

The marketing tradeoff is straightforward: is it easier to get someone to download the Windows 8 App, or to purchase a Nokia phone?  With most of the planet sitting in front of a Windows OS, and using a Microsoft browser, they would seem to have a lot of leverage for promoting a software download.

Why won't Microsoft do this?  Because it implies that the OS is no longer important (the App would run on Android!).