This is a ******** argument. Is an OS a product? Of course. Does it do anything by itself? No. You need hardware to go with it. Hardware with an OS is in combination, a usable product.
Not sure where you're going with this and how this applies to anything I commented about.
You might want to take a second look at what I was responding to, it was geared toward the comment regarding how MS doesn't have a monopoly and my argument was, while there's technically other OS's available, due to how Windows is licensed/distributed, it doesn't readily compare to OSX and does share many similarities of being a monopoly as there's no other entity doing the same thing (or remotely like them).
Can any consumer go into a store and have a choice of a computer WITH an operating system? Yes... side by side in a lot of stores. Corporations? Sure... same thing with numerous IT suppliers.
Again not sure where you want to go with this. You can't go into a store asking for a brand new Sony laptop preinstalled with OSX. You're limited to choices based on licensing and what the company chooses to offer. Anything else is soley up to the user to decide.
You give reasons why so often Microsoft is the choice in that case; that OS X isn't licensed for non-Apple branded hardware, and that linux is largely unsupported and/or unsuitable for end users.
The difference is in the support. Linux is open source and free. If you choose to use it, you're largely on your own to provide and seek support should you run into any issue you can't resolve alone. Most of the support you'll find for Linux distro's are primarily user-to-user.
Microsoft divides their products between retail and OEM with the key difference being that retail products are supported by MS directly, if you have an issue they'll help you for as long as you need over the phone. OEM requires you to acquire support from where you bought the OEM product, not MS (for example Dell, Lenovo, an authorized OEM partner, etc.)
OSX is licensed for only approved Apple hardware, should you need support, Apple is there. Should you decide on installing it on non-Apple hardware (i.e. hackintosh) or in a VM within another OS, Apple has no obligation to support you even if you bought a legit copy of OSX.
Redhat Linux was the first of the open-source OS's to be contrary to the lack of official support, they were the first to sell retail box copies of their distribution where the cost was purely about having an official support center to help you should you need it. So while the product was free, you were pre-paying for the support.