Consider not the fraction of the market, but the size of the market. How many people have GNU/Linux on their desktop?
Compare the size of the market to the size of the market for various other systems. There were 17 million Commodore 64 machines sold. I suspect there are easily this many people with open source desktops in the world; there are around 10 million users of Ubuntu alone. Does the author mean to say that the Commodore 64 was unsuccessful, was itself dead on the desktop, for having a mere 17 million users? It seems unlikely.
Being the sole desktop option is a hazardous place to be. If you believe in capitalism, you should prefer a mix, you should prefer that users (at some level, potentially corporate) decide which system to use.
I use GNU/Linux: Ubuntu on the desktop, Debian on servers and sufficiently high-end embedded systems. That's not about to change. I'm glad others are concerned about converting people, but only so far as it causes them to make better the software I use.