It all just comes down to preference. People out there will always put down extra money for something more sleek and intelligent looking even though they aren't neccessarely better than the PC.
For example: Mac OS comes with just about everything needed to start editing video/audio etc. with utilities both capable and easy to use. And they don't need to spend extra to buy these programs after the fact. Adding this to the added sleekness and style, people will happily spend that money.
Now that hardware is no longer a deciding factor, It all comes down to the OS and supporting software. Apple has this down pretty well, which is why people are obviously still buying them.
While Mac's OS in my humble opinion is more intuitive and easier to use, Vista/XP has more under the surface. There are tons of "specialized" programs out there for windows when it comes to video/audio editting. All you have to do is look around on the internet and you'll find "free" programs spacifically made for generating HDR images in batch or for correcting distortion with wide-angle images. Most of these programs are made by windows users for windows users. Sure you can duel-boot and have Vista on you MacBookPro, but most people don't get their Mac with that in mind. They want everything installed and ready to be used, no added work like buying extra software or looking for programs online.
One big thing that has been stated before is, Mac is always behind in the graphical power race with PC which is important when it comes to intensive work like messing with HD Video etc.. I love messing around with editting video/audio/etc.. so I got a Sager notebook. Sure it's pretty monsterous for a laptop, but It holds 3HDD's (2 in RAID for fast read/writing), 2 Nvidia 8700 /w 1gig VRAM, 4gigs of RAM, Intel Core2 QUAD 2.4, and Vista for $2,700 over a year ago. You can't get that creative with a Mac, and it certainly can't achieve that kind of processing power(yet).
Also, if you happen to like the OS Leopard..some people have already made it so you can use it on any PC(still being improved).
Sorry for the wall of text.
