I have been using linux for about 5+ years now. And really all the versus are mostly opinions. In some situations the different OSes all have positives and negatives.
The pluses to microsoft are mostly umm .... corporate? Not sure if there is a word for what I am thinking. But the pluses for microsoft, are familiarity, and most companies write their programs (games etc.) for it. Because it is supported by money, you also get advertising, so more public coverage.
Pluses to Apple/Mac is the image of simplicity and sophistication, also with advertising.
Due to lack of advertising linux/unix has been "underground" for a long time. It was mostly used in sever environments due to its massive amount of hardware support, and stability. Over the last decade or so it has moved into the desktop / end user segment more.
The other thing that has reduced some people's understanding of *nix is the wide variety of the distrubutions. A distribution is many things, but easiest way to explain it, is the idea of flavors. You get ice cream. It is ice cream, no matter if it is chocolate, vanilla, strawberry, or chunky monkey. It is mostly how it is packaged.
The other thing which I heard recently that makes sense, is that people grew up using a certain system. Usually a Mac or a Microsoft. So you "know" that system. No need to "learn" it. Most people don't like the other systems because they are different, or because they have to learn them. How they respond, what happens when you press this big red button versus the big blue button.
Okay I am rambling, time for me to goto bed. I am not being to coherent.