I see Microsoft's evolution
While I concur in part with your analysis, I view your main point rather differently. Microsoft had a monopoly on the desktop. It still does. The numbers you quote add in phones and tablets where the company never had market share. So analyzing their desktop monopoly as falling apart b/c of non desktop devices doesn't work for me.
My larger take is this: Microsoft maintains a strong monopoly on the desktop. But the company correctly viewed the desktop as a shrinking market several years ago and began three key initiatives to offset the anticipated decline: cloud, tablets, and reinvestment in its phone business. It's clear the first initiative, Windows Azure, is paying off well.
It's too early to tell whether the Surface will ultimately be an important player or not. And the Nokia acq, having only just been completed, is another long-term unknown.
So, unlike the usual story of a company with a monopoly that was unable to adapt to the new world, I see Microsoft as doing that adaptation uniquely well. Far better than other IT vendors, such as IBM, Dell, etc. have been able to do. I think the company's excellent financial results over the last two years strongly support this view.