While I agree with your conclusions, there is an important fact you ignore: PCs now have less than 50% of the internet market in general, and I suspect smartphones and other devices' share will only grow in future, considering the slowing sales of PC and the increasing penetration of alternate gaming platforms. MS doesn't seem to see a way to stem the flow from computers to other devices, so they are maximizing their profits for the short term.
MS has a habit of showing their hand -- remember when they sold Windows subscriptions to businesses when there were no OS upgrades for years between 2000 and the disaster called Vista?
MS in, is a way, in the same bind they put Sun, et al. in a decade ago: they are now the de facto business platform, and they want to leverage that, even at the expense of their future PC personal software. There is much more cash in selling licenses to businesses than delivering OSes to manufacturers at bulk prices which were sometimes nearly free.
MS is a mature monopoly which does not see any competitors on the horizon -- except for phones and consoles. Otherwise, they would act differently. They know what they''re doing and they expect their PC customers mostly not to care.