Back in the 80s, 90s, and early 2000s, processor technology moved forward a LOT faster than it does today. Moving from 386s to 486s to pentiums, to pentiums with MMX, all that crap back then that made people have to upgrade to entirely new machines every couple of years. Now, the bleeding edge of technology is more in the video card realm, those still move forward FAST, with a new generation with significant upgrades coming every year, but it's a hell of a lot easier to just slap a new video card into your machine every other year to keep up than have to build an entirely new PC because your CPU is outdated and your motherboard isn't compatible with new ones, like back in the day. Hell, the Intel i7 has basically been the best all-around desktop processor for about 5 years now. Sure there have been multiple versions and revisions, but it's still an i7. I don't ever remember a processor generation lasting that long at the top of the heap in the history of PC gaming. I have friends plugging right along doing high-end gaming with their i7 systems built 4-5 years ago, just with new video cards now.
And as to the worries that the new consoles will push PCs forward quicker for a little while...I just don't see it. I can't remember a console generation since the dawn of 3D accelerated graphics(around PS1 launch) that is already so far behind the curve compared to a PC at the launch of the console life cycle. These new consoles are high-end PCs from like 3 years ago. They are currently mid to low-range PCs, so there's already no need for any catch-up in the PC world, we're already significantly ahead of the new consoles.
I think the area to keep an eye on will be mobile technology...that could push drastic changes to the PC gaming market. We could see a big push towards touch-screen monitors over the next few years, and definitely a push towards higher than 1080p resolutions becoming the norm. I'm not going to do the math, but PC monitors in general are woefully behind the top-end mobile devices in PPI. 1920x1080 looks friggin amazing on a 7" tablet, not so much on a 24" monitor. 1440p is just the first step, I think we'll see a real push towards 4K gaming on computers during this next console generation(next 5+ years)