People who are using tablets don't want to look at grainy big screens. These screens look blurry. Stop in any store and check out the all-in-one Win 8 touch desktops. Their screens are awful.
And yes blah blah blah higher-res NON-touchscreen with mouse -- but going back to a mouse after touch? That's another step back.
Haswell reportedly has enough power in the GPU to support high res screens using just the integrated graphics - so we should see better screens in 2013 H2. Samsung and others have already announced some incredible laptop screens for upcoming devices.
The longer lifespans of PCs and laptops combined with the popularity of smartphones and iPads is a more likely reason for the drop off in sales.
Microsoft doesn't add anything new. Windows 95 was appreciably better at doing what people already did, there was reason to upgrade, and Windows XP took that even further. Ever since then they've been pretty rudderless. Windows 7 doesn't offer anything that Windows XP can't already do, apart from the new theming. At least it's inoffensive, though, and lets you do whatever you want to do without putting up a fuss.
Windows 8 is something nobody wants or needs, it's a very hard sell, and it's even more bizarre that Microsoft would be pushing so hard on touch into the market that least wants it: Corporate IT.
I said desktop. People sit further away from laptop screens and at a totally different angle. Win 8 emphasizes touch, and all the AIO touchscreen desktop screens I've seen are too grainy to look at compared to tablet screens. Even if the pixel count is the same as a laptop, the pixels, obviously, are a hell of a lot larger.