Hard to gauge really, especially when you've got the likes of Balti's and PC Planet selling an AMD triple core with a GT 740 as "the ultimate gaming experience".
Here's a question, is it possible that more and more people are building there own PC from scratch as PC gaming becomes more popular? Does this count towards PC sales?
My old 2500k / 290 / 8gb combo still plays everything I want at settings I find acceptable. Stagnation in the hardware industry is the cause of this, remember when the 8800gt was launched? That's the kind of stuff we need again.
PC game evolution slowed massively 5+ years ago so no real surprise sales have slowed especially since PC hardware prices remain mental..