The problem is that the author excludes an iteration or two of Mac OS X from the final cost of ownership because he didn't deem them worthy for one subjective reason or another. To make matters worse, he then includes premium Windows services on top of the cost of a Windows license, such as yearly Norton AntiVirus subscriptions and yearly spyware + security cleanings from Geek Squad. While there is certainly an easy argument to be made for the virtual necessity for some kind of security and virus software that (amazingly) isn't included with Windows itself, there are plenty of similar services available, sometimes with free and open source alternatives, which cause me to suspect the author of seeking out the most expensive services he could find to fuel a blatantly biased opinion.
Posts like this that use underhanded techniques and shoddy math to prove a biased point aren't helping the Mac community. In fact, they're making it look even worse because, once found out, they are (rightfully) transformed into key evidence for clueless Apple fanaticism, which can easily harm the reputation of almost anyone with something genuinely educated and relevant to say about Apple or their products, whether it's a good or *gasp* unpleasant statement.
These wholly inaccurate and misleading articles need to stop if computer users are going to learn the genuine advantages (and even disadvantages) of Apple and their products. Lying to grab attention for Apple may briefly taste sweet, but helping consumers make an educated choice (no matter what the outcome) based on pure, true merit takes the cake.