Yes, BUT...
When you start to get into the 3-4 year age range with any high end computer, the parts supply can get a bit funky. I have a 2011 socket type motherboard with an i7 in it, the motherboard can take an "extreme" processor (6 cores instead of 4, larger caches), but those chips are still 700-1000$ even after all this time. Once you get into the super high end, you'll pay, oooh you'll pay.
If you want the newest hardware to work flawlessly at the highest possible speeds out of some of the newer graphics cards and memory, you generally end up having to upgrade the motherboard, which means upgrades to the CPU, RAM, and most likely the hard drive.
I'm looking at getting a 144hz Gsync monitor at some point, but to utilize the low response time I'll need to upgrade the GPU, so the whole thing will cost 2X what I want for just the monitor upgrade. I've delayed that purchase, perhaps indefinitely. I can totally see how its possible to go over-board spending 2k on monitor + graphics card, another 1k on a CPU, 1k on motherboard/case/memory/HD, and 1k for some company to put it together and ship it to you.
While you are generally correct, the only parts I'd expect to potentially fail, or start to fail, after 3-4 years, are the power supply and the cooling.
Power supply - buy better power supplies... capacitors do age out, but 3-4 years is short. Definitely not unheard of, especially on budget supplies. Actually, relevant to cooling - power supplies should have their own fan, and if it starts to fail, the rest of the supply may die quickly.
In any ever, a decent PSU is somewhere between $100 to $300 depending on your needs. ~$300 buys a 1000+ watt 90% efficient monster with top notch ratings and an expected lifetime of over five years.
Water cooling systems should probably be replaced once in a while just in case, or at least inspected. Spinning fans often have bearings that shit the bed - after just two and a half years, one of my 140mm fans started to grind, and I couldn't find a proper replacement, so I went for a $40 upgrade for two new fans (and kept the old working one as a spare.)
Nothing else should fail on that timeline...
Unless you really enjoy overclocking processors, in which case, computers are just a hobby you sink money into regularly, and processors become consumables. If that's so, then, meh.