I guess it's the home versus work markets.
Home users will like Macs because they appear to be easier to user (I haven't used a Mac since 1988, so I'm somewhat out of date). Frankly, if my mother came to me to ask what computer to buy, I'd probably tell her to get a Mac.
Business, on the other hand, uses Windows. They won't change because it would cost too much. They've already invested a lot of infrastructure and training. MS would have to screw-up Windows
very badly to make business change.
If Macs got very popular, MS would start shipping more apps for them. I'd be happy to write Mac code if MS made a version of Visual Studio for OS X