My Dell laptop had 13 motherboards, a new screen, keyboards...just about the only part that was still original after 3 years with it was the hard drive. My mac mini, for comparison, is still all original (except for the 100 gig HDD upgrade and added RAM), but it's been flawless.
I dunno if you've ever heard this analogy, but if you were an alien and visited a hospital, you would think that everybody on the planet was sick.