You seem to be confusing 'Windows' with PCs
All my PC based servers run Linux of one form or another.
In fact, one of my home PCs runs Linux as well.
This thread is about the relative costs, we have done the 'which is best' thing to death many times over the last few years.
Personally I could not switch to a MAC, cos the software I depend on is just not available for it, (no, not the obvious stuff - the specialist SEO type stuff)
I am sure that most MAC users have a similar problem moving in the opposite direction.
Its irrelevant - they are both just tools - work with what you are familiar with and relax on trying to convice others on what is basically a subjective view (whichever camp you fall in).
Regardless of the 'mine is best' type arguments, the article suggesting that MACs are cheaper is still just plain misleading on something that is NOT subjective.