I'm preaching to the choir here, but the obvious third case the author omits is 'semi-technical folks who don't want to deal with the friction of a new environm

I'm preaching to the choir here, but the obvious third case the author omits is 'semi-technical folks who don't want to deal with the friction of a new environment', which is not so offensive. And 600 million 5+ year PCs seems like a low number...