It is an interesting number, but because it's wider than the scope of just the "normal PC" sitting at home.
When you go to train stations or airports and see departure or arrival screens (not the old fashioned LED / written text ones) - they if they are computer driven, will likely have an OS behind it, and these are commonly easiest with windows.
Business will always favour windows because Apple with either be too expensive or not suited to their needs, so the level of Microsoft support suits them, that and Microsoft is specifically geared with all of it's packages to sell to businesses, they're "all in one" packages for them. Also many colleagues of mine who support for large businesses often find that they get more issues from Mac networks than Windows networks (but that's not my words).
Linux - whilst one could argue is "technically" the best due to it's resource light nature and coding capabilities, it's only needed by those who need those capabilities, and is usually favoured by those who don't really want to know much about computers, which is where windows falls in.
CNC machines in manufacturing organisations will have an attached computer to run the CNC programs, which all have a core OS behind them, which is usually windows for the same reason that it is best suited for that function.
Also Windows was released before MacOS - so naturally the market will stick with what comes first, and being as Microsoft has been sustainable over the years, people will stick to using it and making programs and hardware to suit it.
I think it becomes a lot clearer when we don't just look at it from a "Windows on a Computer at a desk" function. Because it really is used on many more things.