And beyond Office, if you're a non-technical business with employees in the low dozens, pretty much no one is even interested in selling you a full stack of software + support besides Microsoft and its approved partners. Pretty much any office with like 25 people that's not in design or tech is top to bottom Microsoft, not just Windows and office but inventory, HR software, whatever else all running on MS and sold by either a Microsoft subsidiary or might-as-well-be-a-subsidiary channel partners.

That's the vast majority of offices. And the lower number that are large/savvy enough to be pickier on backend systems still buy Windows and Office licenses anyway.

On the flipside, it's hard not to see mobile platforms eventually cannibalizing Windows from below, the way PC platforms (like Windows and GNU/Linux) eventually cannibalized minicomputer platforms, which in turn had cannibalized mainframe platforms.