I have to weight in here.
For graphics work, the Mac absolutely does NOT have the edge at the moment. Pretty much everything is out for Windows as well, and Windows doesn't have the problem of Rosetta-emulated software at the moment (crippled Photoshop, etc.).
However, video on a Windows notebook computer is not an easy thing to do. In my opinion, it's pretty much broken, which is to say that a guy with two computer science degrees can't get it to work.

I'm sure there exist notebooks out there that just work, but more often than not I've seen big problems trying to get cameras to talk to PC card / Expresscard firewire cards.
For example, I've had two Thinkpads, and both of them *sometimes* talk to my A1u when using a Firewire PC card. Expresscard firewire ports don't talk to my video cameras, though, and neither of the computers have ever worked with my Z1u even when I've installed a new OS on its own partition just for video.
Two weeks ago, my Thinkpad stopped working altogether with my A1u. More often that not, testing involves voodoo that people on the web swear by. "Oh, you have to turn your computer off, plug in your camcorder, turn the computer on, turn the camcorder on..." etc. etc. This is crap! Plug it in, and it should just work. It doesn't.
These are not isolated incidents. Many other people I've met on the road who try to use their notebooks as editing machine report similar problems.
My desktop PC works just fine.
Still, I'm getting a Mac, and will suck up the slow Photoshop issue until Adobe releases Universal binaries.