Am I the only one who doesn't have this problem?
If anything, my PC works better after a few months than it did with a freshly installed OS. It's just more functional.
If your HDD degenerates over time, buy an SSD for a system drive. It will solve a lot of problems in the long term.
With that said, my Spinpoint F3 was going strong for almost 2 years.
The only time I need to do a fresh install is when I upgrade major components of my PC, replace my main drive or upgrade the OS.
Keep it clean, use PC condoms, stay safe and everything will be fine. Regular checks also help and make sure that you don't bloat your PC with unnecessary crap.
There's only a handful of programs you have to use to keep your PC clean on regular basis and defragment your HDD every now and then.
Oh yes, and check your start-up regularly, as Jimlad suggested, it is often full of useless stuff that you don't need running every time you start your PC up. CCleaner has a tab for it, you can use MSConfig too.