I think Windows is all people ever know, so they never bother to look beyond. And I'm sure that they are many that think all the problems that are on Windows, must be on the mac. Prove it, well, just look at everyone that comes here and says what's the best virus app for mac, or how do I defrag the hard drive, or what program do I use to get rid of spyware. You would think that this is why switchers switch in the first place, guess not, but many Windows users seem to overlook the pluses of having a mac.
Mac is still living down a legacy of overpriced and underpowered computers from the mid to late 90s. It lost a lot of momentum during that time.
Most people still think of Macs as 'easy to use' computers for people who don't want to mess with computers much. Problem with that is that most people want to mess with their computers.
The Irony is that Mac is now capable of giving the best of both worlds - you can really get down and dirty with command line on a Mac running OS X. Mac comes with Perl, Python, gcc and host of other programming languages and powerful unix command line utilities as well as all the standard C and unix libraries. Want to learn C? Pick up Kernigan and Ritchie's 'C' book and you can go to town on a Mac straight out of the box. To get that on a PC, you have to download a lot, and pray a lot, and figure out a lot of non-standard PC garbage. Or get Linux, but then you don't have the easy to use part for when you really don't want to get down and dirty. By comparison to Windows, OS X will attract people at the bottom and top of the technically savvy chain - the most technical and the least technical.