And these are good questions. I started to reply there, but decided I'd muse over here at greater length.
I have a friend who's thought occasionally about getting a Mac instead of his Windows machine -- he doesn't have any problems with Windows (that he's talked about), but he's comfortable with Unix and likes Apple's designs and so on and so on. And we can even set aside the argument about hardware price; if you're buying a new machine from scratch, the difference is pretty sharply reduced, particularly if you're buying a turnkey PC system from a big name vendor.
If he made that switch, though, the hardware cost isn't the issue. He would have to buy new copies of all of his programs. He has Corel Painter. He has Microsoft Office. He has an earlier Adobe bundle which is pretty much what became the Adobe Creative Suite.
So suddenly, that's $1500 more to make the switch, just based on those programs. And that's going for the "standard" version of the suites--tack on another few hundred if you go for the full shebang. And there are probably lots of little other programs he's bought over the years--not games--that add another few hundred. (He also has Maya, which is another $1999, although that's kind of an unusual case!)
This works both ways, of course. PC users can go on all they want about how the new AMD SuperChicken64 will run twice as fast as my G5, let me use ten times the memory and a better video card and do it all for two-thirds the price. And that's all great, but unless the SuperChicken comes with pretty direct equivalents to $1800 worth of software--yes, I just added it up--any theoretical savings switching to it is more than negated.
But what price sanity? is still a good question. Statistically, even Windows gods are increasingly risking being bitch-slapped by viruses, spyware and all sorts of other nasty crawlies. And even if they're not, Windows--both the original line and the NT line--is subject to what I called "creeping crud syndrome"--just through normal use, things subtly get messed up, until eventually you reinstall your operating system in frustration. I know Windows users who never seem to have any serious problems with their OS, but they appear to be in an ever-decreasing minority.