This is interesting.. I'm doing the Android Coursera course in Jan along with a few others from work. Part interest, part wanting to develop skills further, part more prospects.
I sit 70-483 (Programming C#) next week and I have no intention of doing any more. I really fancied doing my project in Xamarin.. although I've got more chance of going to the moon than being able to afford to use that with the features I need in the current climate.
I keep getting priced out of what I need by MS. And the whole time the competitor is gaining ground, becoming more interesting, seems more appealing and now there are more jobs available in my city. To top it all off, all the tools I need for these are free..
If you go to Jobsite and search for Android, there are now more jobs than WPF, and almost none for Windows 8. That shows you the direction the market is going.
I would recommend doing Android development, as commercially, that is the platform you can make money on. Steve Guggenheimer gave "short-shrift" on the subject of the commercial prospects for 3rd parties on Windows in a recent C9 video, and said "there is a discussion going on".
This is all the information you need to see that commercially, Windows is destined to struggle because it does not provide the commercial ROI that Android does as Microsoft still believe people are going to pay many thousands of pounds for development tools, then give away a third of any commercial success. You don't need to be an accountant to do the sums on that one.
I might just join you on that coursera course.