x86 is an architecture, like ARM, that has seen many contenders come and go over the years. Intel's dominance is because of engineering excellence, albeit coupled with some questionable business practices. Show me an ARM device that compares with a Core i7-950. Show me one that compares with one with 3 of the 4 cores turned off.
Microsoft, for that matter, has had versions of Windows for alternate platforms going back well over a decade. Those platforms got abandoned not out of some strategic affinity to x86 (much less to Intel), but simply because they didn't offer the advantage to be worth the bother: Instead they were pursued during the "the Future is RISC" era and it was preparing for the purported demise of x86.
As to manufacturers that were "Microsoft exclusive", show me even one. Such a thing hasn't existed in years.
There is nothing I have ever read on Asymco that isn't full of glossy big conclusions, yet absolutely falls apart under any scrutiny at all. It is garbage analysis.
I love the smartphone era. I love the fact that embedded chips in everything from your HVAC control to your PVR to inside televisions and cars, etc, are all massively benefiting from this explosion of reasonable performance, low power devices.
But let's get real. The only reason x86 is behind right now is because ARM had been working on low power processors for years, and the chips came up that it was the hot area. Intel isn't sitting on their hands, though, and I have no doubt they'll have some killer solutions in the very near future. People are so quick to jump to conclusions though, carried on by simplistic analysis of the sort that Asymco performs.