Until Linux is as user friendly as Windows, it WONT be as popular as Windows. You have to realize that the majority of computer users ARE NOT as experienced as most here. They cant use Linux because it isnt user friendly. Windows makes it so darn easy to overcome problems, learn new things, etc. that it is the OS for beginners.
Im not saying Windows is better than Linux, just that until Linux makes their distros user friendly enough for the average computer user to install and run without ANY problems....then it wont be as popular as Windows.