OS X is free now.
http://m.computerworld.com/s/article/9110179/Apple_sues_Mac_...
It is folded into the cost of the hardware at this point. So yes I can see what you're saying in terms of profits on the OS vs another OS. But it is not free (as in beer) exactly.
And you've still paid for the hardware, which is where the price is wrapped into, since about Snow Leopard.
Not saying it isn't good (I am a half-time Mac user). But calling it 'free' is not entirely the case. I used to get pretty annoyed at having to pay for a new version of OSX from 10.2-10.5 every year or so.
I do cover the cost of the software on the hardware, but the same is true for about any device I buy.
The thing is: Microsoft is trading software as a good. Even if I buy a machine with Windows, I can actually, in some legislations, ask for my license money back and my machine gets cheaper. So I didn't get Windows "for free". So their market is software and should be counted as such.
Apple sells hardware as a good and doesn't ask for any fee for the software that comes with it. So that element is free. Even if I would ask for my money back, the answer would be "sure, here's your 0 Dollar".
Yes, it is an accounting question, especially because in the Microsoft case, your vendor pays the fee for you immediately.
You cannot buy an OS X license anywhere anymore.
My point is that it is not 'free' in that you can't freely download and install it onto a computer ala Linux/unix. You can not sell new computers with OSX preinstalled. That more or less defines that it is not 'free' when compared with an actual free OS.
Not being able to buy a license without the hardware doesn't make it free. It just makes it tied to the hardware. There is still a EULA (End User License Agreement) and thus a License.