When you compare spec to spec, there is always a Windows machine that cost less, quite a bit less, than an Apple. However, when you add in build quality, and check out the reviews on some of those 'great deal' Windows machines, the price gap starts to close rapidly. Either way, the cost counters on both sides have always been able to twist the argument whichever way the wanted. Only the person buying the computer can decide which combination of features and form are worth it to them.
Apple just doesn't build low end machines. They refused to even consider the netbook. Instead when it looked like people really did care about the size, they flipped the concept onto a premium machine.
Another thing to consider is that with an Apple machine, you can still run Windows if you're willing to invest in the software. The opposite is kind of true, but in reality only true for those willing to tinker, a lot.
The biggest benefit to going all Apple is the tighter integration you'll see between your devices and computer, mostly via iCloud. There are quite a few things you simply can't do on Windows, and several that are a lot easier on the Mac. That is even more true with Mountain Lion (the newest version of OS X), and it will tighten up again with iOS 6.
iTunes works better too, though it's still a franken app.
I am admittedly Apple biased, so keep that in mind. I do like to think I came by it honestly though. I spent several years supporting a Windows network.
