More like every 3-4 years for consoles. Secondly, console game devs always develop for the consoles capabilities so that's a moot point. Lastly upgrading a console every 4 years costs less than keeping a gaming PC current.
2/3 objectively false, though I will admit you need to do a lot of research and put a lot of effort in to optimize a cost/longevity PC build. Whereas a console is just bought and done.
The fact that most games are built to run on consoles basically guarantees that you can just build a PC marginally better than a console for about the same cost and not upgrade it until the next console generation.
Also this entire conversion completely ignores the indie market and some big name releases that are still plain enough that they could be run on a PC from several years ago. And there are THOUSANDS of old games to play too, it's not like you're bound and gagged on new releases.
Edit-
And I don't HAVE to keep upgrading my PC, I can stop whenever I want!
No one can keep pace with current generation PC parts without spending thousands a year- but that doesn't mean you're unable to play the latest games. PC exclusive titles generally do a good job of supporting the oldest hardware possible (looks like crap but you can play) and it's usually a good 6 years before you can't play games on the low-middle graphical settings. Longer if you overclock.
If you choose to not upgrade for 6+ years then yeah, you'll eventually fall behind the PC game curve, but does that make your investment up until now a waste? No, especially considering the build is likely going to be much better than current Gen consoles... So the downside of not keeping any pace with new hardware is your rig will only play games x% faster and prettier than consoles instead of 1.5*x%! ::sad face::
And honestly there aren't that many big budget PC exclusive games lately so there's not really a curve to keep up with. The most interesting new releases are indie and those generally don't require much power to play... So all you need to do is aim a bit higher than current Gen consoles (not hard or even expensive to do) and you'll be fine.