Oh dear.
Comparatively speaking, my PC which I built instead of getting an iMac (in 2008), runs better than the equivalent-priced iMac from the same time. Just because you choose to not consider a custom-built PC as not being equivalent does not make it so. We are talking about making a computer from the best bang-for-buck technology that is available at the time. You carry on in your Dell vs iMac bubble but the real equivalent of an iMac is a custom-built PC.
I've built PCs, as I mentioned earlier, so I really have no idea what this Dell vs iMac bubble reference you keep mentioning is all about.
The person who goes to the Apple Store and says "I want that one" is most likely not going to consider building their own PC. One is pushing the buy button on a website, the other is researching and selecting components and building their own machine. If you want to consider those things equivalent, to each their own I guess.
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Actually, my self-built PC is ten years old, and still runs fine... but it's still on Windows XP, haha. I'm amazed, given how hard I pushed it prior to my Mac Pro.
That actually brings up an interesting point, I'm able to run Lion on my iMac with no real issues where I'd imagine Windows 7 or VIsta would choke a lot of older PCs. It would be interesting to compare things using the relative OSs of their time as the more recent OSs are way more taxing on the machines.
As per your other comments it sounds like one of those YMMV kinda situations, I've had zero issues with my iMac for going on five years. The ideal situation on something like an iMac is probably to cycle a machine every three years after AppleCare expires, you'd still do well on the resale value and would get rid of most of the risk.