Earlier quoted context omitted.
Your point is valid, but it's becoming less so. The web is taking over more and more of what used to be desktop territory, and the OS is becoming a device driver for the internet. There are plenty of people now who just need something that will run a web browser (granted, there are also still plenty who have to have MS Office or whatever). The more cheapass the PC, the more of a difference the Windows Tax makes. $50…
The point wasn't whether people do or don't need Windows software, it's that you can't just throw Linux systems on the market unless the consumer feels they have some compelling reason to buy one. And MS does scale their license prices based on the system costs, but I think you've demonstrated one can always find a cheaper PC without switching to Linux.
There are also large organizations that would like to cut costs wherever they can, and can't be expected to make up the Windows tax by installing crapware like a vendor can. The city of Munich is the most well-known example of a big player switching to Linux. The effort was not a complete failure but was something of a disappointment - I don't think Munich ended up saving any money when you consider the labor costs, etc. But if Linux had been ready and the transition had been more successful, you'd see a lot of imitators following Munich's lead.
But it's probably a moot point anyway. I think Android will end up swallowing the PC market like a classic disruptive technology and stealing Linux's thunder anyway.