They're simply different. On the whole, Mac hangs together more stably than a Windows PC, and the software is pretty good.
However, I also have some Mac software on my PC now - I compiled and installed Handbrake, and also I'm trying out Safari, Google Chrome, and quite a variety of Windows, Mac, and other software - mostly open source.
They all have strengths and weaknesses.
For me, the killer difference is price. Not spending enough to buy a new car means I can't get a macPro - and when scaling down to my price range, I found that Windows PC's offer sooo much more computer for the money.
I then installed ubuntu as a dual boot option, and stopped XP from accessing internet - took a lot of security issues away, but I can still run any windows software either by booting windows, running from my windows partition (it opens in WINE), or installing it inside a Virtualbox running inside Ubuntu.
I'd like to have iTunes running natively on a mac - but it's just not worth the extra money! Sorry folks. I have to go with PenguinPC, because you can't combine all 3 without paying for the Mac! Mac loses out.