Some people have a higher tolerance for dealing with anti-virus issues, updating McAfee, etc. I can't stand all the busy work re: antivirus stuff on Windows. This is one of the main reasons I use a Mac. That and I much prefer the OS X GUI to Windows. I quit using Windows years ago, and I am so much happier now. When Vista came out, I bought a laptop. I sold it 6 months later, as I hated it. I know Windows 7 is an improvement, but my guess is it is still the bloated, slowish OS that is was under the name Vista.
That, and the multimedia tools for photography as so excellent on the Mac. Aperture, iPhoto, Lightroom 3 (I know it's not Mac only like the others), Photoshop. Also, I could never live without Photoshop, I use it everyday. From batch resizing images, to cloning dust, blemishes on portraits, all of the awesome plugins for Photoshop like Nik filters. I have Lightroom 3 as well as PS and Lightroom does not have much in the way of the cloning, retouching tools that Photoshop has.
Photoshop really is not all that complicated, and you can use it quite happily without using 80% of its features. The ability make layers alone is extremely useful. Not 100% necessary, but the are countless books on Photoshop (Photoshop for Photographers) that will make using it much more enjoyable, and make you more productive. Once you learn just the few things that you will use for your images, things that really are not available on more "photo browser" oriented software like Aperture/Lightroom, you will find Photoshop Elements to be too basic.
Lastly, it's a great time to be a Mac user, will all the excitement with the iPad, iPhone, cool new MacBooks, etc. And OS X keeps getting better and better. If you really want Windows, why not dual boot or run it with VMWare Fusion, which is such a great emulator, that you one you start your Windows Virtual Machine (or Ubuntu VM for that matter), it will have you thinking that you booted into Windows.