As an example to illustrate my point, let's just say that the aforementioned J. Random computer geek just has to replace his CPU fan, either out of necessity, or as an excuse to open up the computer for some reason or another. Now what's going to happen here is that Mr. Geek is going to see that it's awfully crowded in there, with all that stuff sitting around. So, needing more room, as many computer users do after a while, our friendly neighborhood computer geek goes out and buys a new case to put all this stuff in.
After hours of transferring and rearranging stuff, finally everything is in the new system. But, now there's a little too much room in there. Of course, anyone who's up on their old maxims would realize that nature abhorrs a vacuum, so something's going to be filling up all that space before too long. In this case, most likely what J. Random Geek will be filling this up with something like an extra hard disk. This happens to fill up the extra empty space inside the case, but also creates another vacuum... a major increase in available disk space. Seeing this, the geek now has the inclination to come up with a suitable excuse to fill this up with stuff. Most of this space will probably end up being filled with games, since that seems to be a popular thing to fill up hard disks with.
So all of a sudden, there's a whole hard disk loaded with all sorts of new games, and all that bloated code piling up on the hard disk seems to slowing things down quite a bit. And of course, if the system is slowing down, Our friendly neighborhood geek is sure to conclude that something in there needs to be upgraded. Most likely this will be RAM. After all, it has been said that you can't be too thin, too rich, or have too much RAM. Driven by a neverending quest for performance, more and more RAM goes into the system, until finally, the games all work, but they're slow...So next, the motherboard and CPU get upgraded. Finally, they run decent, but now they look bad. Whoops Off to the computer store for a new video card... Now, the games run fast and look decent, but suddenly every twenty minutes the system crashes.
This didn't seem to happen before the new video card was put in, so there's already a likely culprit here. A quick flame to the video card manufacturer's tech support reveals that it's not a faulty video card, but that the bus mastering support or some other such technical jargon, which basically implies that the only was that Mr. Geek here will ever get this friggin' thing to work properly is to replace the motherboard. OF course, this gets done, and now things are working properly, but since now the new motherboard supports a much faster CPU than the last one did, he goes out and gets one of those. It is at this point that he begins to realize that by doing all of this upgrading on his system, suddenly he has reached the point where he could just about put the old system back togetherwith all the pieces left over from upgrading this system. He pauses for a moment to contemplate this, then proceeds to install the new CPU in the machine. When the machine is booted up, however, there is an unmistakable whirring noise that seems to indicate that the cooling fan is going bad in this puppy... And the rest, as has been said so many times that I lost count many issues ago, it history.
And thus we see how even the slightest little hardware replacement or upgrade does in fact wind up becoming a full overhaul of the system, guided only by the egos if the computer industry and the pocketbooks of the people who got richoff this process that ironically, they happen to be the victims of themselves. Of course, the unwashed masses tend to prefer the "wait until it sucks, then replace it" way of upgrading computers, probably because of the fact that Packard Bell, Compaq, HP and their ilk have a tendency to use proprietary hardware that costs loads to replace (it has been reported by one of my tech support customers that many Compaq machines won't work with the memory you buy at a store, and their memory costs well over $100 for 16 MB... Can you say "Highway Robbery"?) Of course, to the diehard computer wonk out there, it's a lot easier to just keep upgrading the ones you got, and let new systems form in the wake of all the leftover parts. That way, one doesn't have to absorb the entire cost of a new computer all at once, and even though the newer computers end up beiong older equipment, eventually these ones start being upgraded also. And thus the continuous upgrade cycle continues, either until Moore's law expires (this is expected to happen sometime around the 2030s, if the Millenium bug doesn't end society as we know it) or until someone gets really sick of it, throws all the computers out the window, and heads to the woods to be a hermit.