Except for RAM, the vast majority of PC users will never fully max out their machine. They won't even get close to what the CPU can do. Even 10 years ago when someone asked me what kind of PC they should buy, I would tell them to buy the oldest machine they can find with twice as much memory as they think they need -- because in my experience, lots of RAM contributes more to the longevity of a machine than loads of CPU.
The plural of anecdote is not data, but I figured I'd lend a me-too to support what you're saying --
I have a gaming system. It's 2 years old. Core i5 2500k, overclocked at 4.8GHz, with 16GB of RAM. I bought it for $1000, 2 years ago, and haven't needed to upgrade anything. Not even the video card. It's currently connected to the TV via HDMI, with an xbox controller connected to it, and I play Steam games on the big screen with it. It'll be a while before it needs any kind of upgrade, in part because I've gone to Linux on the gaming machine (was originally Windows 7), and in part because since buying a Playstation, I don't see much point in playing the rat race on the desktop.
I'm currently typing this on a 3-year old Dell Vostro v130n, which came with Ubuntu 10.04, 2GB of RAM, and a dual core 1.2GHz Sandy Bridge celeron. The version of Linux that's on it has changed to something much more modern, but other than that, it does *everything* I want on a laptop. I literally cannot see any reason to ever replace this laptop before it dies a horrible death. That could happen as soon as I click submit to this comment, but it could also be years before that happens. My next laptop will probably be a chromebook... wiped for my preferred flavour of Linux, but the majority of computer users wouldn't even need to do that, because ChromeOS does everything they want with their computers for a fraction of the cost of buying a Windows machine, let alone something like a Macbook Pro or Air.