The magnificent idiots who think so haven’t understood the real shift of the market. No, it’s not Windows’ modern UI that slows down the market. Consumers do.
Consumers don’t stop buying PCs because they are scared of a new OS, they stop replacing their old PC because their iPad or Nexus tablet does the perfect job for most of what they need.
Proof that Windows 8 is not the culprit, Apple’s desktops are also suffering:
“Apple fared better than the overall U.S. market, but still saw shipments decline as its own PCs also face competition from iPads.” Source
The real question raised by the current situation is: How many people really need to create, how many just need to consume?