Ignoring for a moment whether Windows 8 is selling well compared to previous versions or not, it certainly can't be described as a "popular, must have product". There is no sense out there in the market of a clamour, no baseline need
for people to go out and rip and replace what PCs they do have with shiny new ones running Windows 8.
But, we do know that they are going out there and buying smartphones and tablets -- i.e. post-PC devices -- in astonishing quantities.
We can umm and ahh and cogitate as much as we like as to why this is. But regardless of the relatively attributes or merits of each product it all reduces down to this one, basic point: products that sell, regardless of the market, are likeable