I don’t think anyone really expects Linux to take over anything…
I just spent 2 weeks trying to create a simple network share, remote desktop and assign the correct permissions and whatnot; never got it working right. I also couldn’t get most of the CLI commands to actually do anything and that was even after I memorized everything I needed to configure. I finally gave up and installed Win7 and I did everything I wanted in less than 40 minutes, including installation.
I like Linux, specifically debian and ubuntu, but I don’t think I could use them regularly for anything other than basic tasks and browsing the web.
Bottom line… if Linux wasn’t free, my guess is that almost nobody would use it.