Comp parts last as long as they always have - if not LONGER.
The only problem is that software devs (looking at you, MS) make OS' for new comps (i.e. OEM) - their main market ISNT upgrading people. So, as its being bundled with new comps, they always have an expanding resource cap, rather than a fixed one. As updates are released, the resource usage goes up, making the comp slower and slower.
With no software-side maintenance (boot managing, defrag, CCleaner, etc.), this can all add up insanely fast, so a comp that was fast one year might be incredibly slow the next.
Some good examples of this are my old Dells (yes, I had two
). The first one was from '03, ran a p4 @ 2.4ghz, 512mb of ram, a 64mb integrated Intel GPU and an 80gb HDD. Back then I was a totally new person in the gaming area, so I was playing games like Age of Empires 1, Rise of Nations, etc. Mainly 2D RTS games. My first REAL 3D game was Combat Flight Simulator 3, and that ran at about 15fps @ 640x480 on the lowest settings - and I didnt notice settings existed (last PC games I played were in the mid 90's - there WERE no settings!). That comp also was running Win XP x32.
I had it up until last march, when I FINALLY replaced it. At that point, it was still running the same instal of the same OS, had zero games installed on it, and I had done everything I could to make it "fast" again. However, it took about 2 minutes to load windows, 3 minutes to load Outlook, and about 30 seconds to open up IE. i.e. things that should not take time.
Basically what had happened was that Windows kept releasing updates which would only use a few KB more ram, or a few more CPU cycles. Over 7 or 8 years, that adds up a LOT, especially with only 512mb ram and a single core, 2.4ghz CPU. Amazingly it was the most reliable PC i've ever had. I had ONE BSOD in 8 years, and one freeze-up when I left a game idling for 5 or 6 hours in a 3D scene (i.e. using the GPU).
The same thing happened with my Dell from Jan 2006.
A long time before this, they didnt release updates all that often, and even then they werent even needed. An OS would come "as is" for the most part.