The headline is a bit misleading given that it's compared to the same point a year ago, rather than the last six-twelve months, or even just a month or two prior.
The article itself states the trend is shifting toward more lightweight devices ["The strong performance of Windows 8 notebooks with touchscreens, where Windows 8 truly shines, offers some reason for optimism,"] so it shouldn't be any surprise that PC sales are down quite a bit from the same point last year--especially with many people still struggling with an economic downturn.
I get that a lot of people don't like Windows 8--nothing wrong with that--but it seems more than a little bias to associate it with a downtroden PC market that wasn't exactly booming before it hit, and make it seem like Windows 8 is the bane of the Windows PC World that will bring the rafters crashing down.
As a point of interest, it'd be interesting to see Apple's desktop sales.