We are legions using ubuntu and Linux. Billion of user not million. Do you think that the number of user is the most important thing ?
The number of PAYING users is the important thing. There are millions of Linux users, but few will pay for software.
Note that windoow maket is going down. Do you know that vbulletin of you favorit forum is running under ....
Linux is a great server OS. But it's not bulletproof or idiotproof enough for desktop. If you switch everyone from Windows to Linux tomorrow, they would be screaming to switch back the next time they try to install a new Video card, new Sound card, or play a favorite game (even through WINE).