"New versions of Windows and sales of new PCs go hand in hand"
"If I'm wrong, and you can prove it, I'll gladly put my hands up and say I'm wrong... but until then I am, as I said, calling bullshit."
You're right, but I think the original poster meant different, in that, (regardless if you're buying new or upgrading or otherwise) with any purchase of a new computer, it is generally accepted you're going to get some version of windows with it at the same time, that is, the sticker price already includes the price of that windows.
This is certainly not an exclusive rule: By far most people are not computer heads, and are not able or willing to change things once it's out of the box. Corporates and home-geeks are not in the same league though, and ARE able and willing to make forced changes either due to requirements, or pure preference. But I'm not quite sure if I want to call them the majority either.
As far as buying a new version of windows goes, agreed, outside of those few oddballs, or perhaps some that have strict software requirements, this is not Apple, people don't line up overnight to buy a new boxed windows version, nor download and install the newest and greatest version of windows "just because". It just doesn't happen.