And you are saying things that aren't true besides. First, peripheral drivers, especially sound and video card drivers, aren't Vista compatible primarily because of more restrictive DRM in Vista, and many vendors chose not to rewrite their drivers to comply, opting to sell new hardware instead than supporting older tech. Thant's because DRM challenges all applications and hardware to detect and deny "stolen" digital content, and if one component isn't playing along it shuts down all subsequent communication between the offending software and the system.
Second, computers from Apple's most popular desktop segment sells for around $2,000, not $5,000, and are hardly overrated; instead they are praised as being some of the most capable and bulletproof equipment available on any platform. You cannot buy anything off-the-shelf from Apple for over $3,500 in any case. Only build-to-order Macs have higher price tags.
Third, once you pay $2,000 for your maximum-capability Mac, what do you have an itch to replace? That's like saying "I just bought this amazing $4,000 Alienware PC with all the bells and whistles, but now I want to spend another $1,000 upgrading parts." And $4,000 is pretty much the base for a high-end Alienware, Falcon Northwest, etc; with similar components -- OK, these PCs usually have $200 more in RAM and a $500 video card, but not worth double the price of a Mac. As is well established, even a bargain-basement Dell with similar insides costs hundreds more than a factory Apple.
Finally, aside from the video cards (which I mentioned previously as being withheld because of market size) and motherboard, everything you can access in the Mac can be swapped Mac-label free, from Intel CPUs to Crucial RAM, from Sony DVD-burners to Seagate drives. You can add more USB, Firewire, IDE or SATA port cards, replace video fans, you name it. Buy 'em anywhere, from PC stores or whatever. Of course many of the internal components are better than 3rd-party makers can come up with (pro-quality internal sound in/out, bluetooth and WiFi components) so there's no market for replacing these parts. But if you need $1,000+ video processors or outboard audio processing cards, they're available.
If your Mac still isn't junky enough to just replace after three or four years, you can upgrade nearly everything. And while PC owners replace their machines far sooner (in part because many non-technical owners throw up their hands and buy new PCs rather than pay to get the spyware off their old ones), Macs' lifespans are far longer, which means many parts don't NEED immediate replacement.
The discussion here mainly tracked what would happen if Apple increased its market share and whether hardware makers would increase availability of upgrade parts. Of course they would; vendors follow the money. So logically, geeky home-builders would have things to play with even if they started from a pre-built framework, just as if you went to a local Frys or MicroCenter and bought a bare-bones PC then added your own upgrades. But the dollars equation puts it more into the custom high-end factory modders ballpark where it's tougher to justify spending the money with all you already get with your purchase.
I'm not picking on you, if you post, have a reason and be factual.