I'll answer for myself, as I have no idea about the author.
For me Windows is disqualified from the start because it's not Unix or Plan 9. The nature of my work requires a Unix environment, and even if it weren't the case, I'd still prefer a Unix/Plan 9 environment.
The various Unix emulation layers available in Windows like Cygwin, SFU/SUA/Interix, UWIN, MKS don't satisfy me the slightest, and even if they did, they'd restrict me to the Unix side of things while on Linux or Mac OS X I most often use plan9port.
I use virtualization all the time, I have to, I can't even chose not to. I am a kernel programmer, doing kernel work without virtual machines is very difficult, for one particular non-Unix operating system I develop for it's even impossible.
But my choice for Unix-based systems is not necessarily dictated by work. I use Unix tools all the time, for everything. Why would I run Windows as my host when my toolkit is available only in a virtual machine and I don't care at all about the tools Windows offers me? It doesn't make any sense, I'd have to run at least one more virtual machine and I'd have poor integration with applications running in the host.
By having Mac OS X or some Unix derivative, like Linux, as my host I have my toolkit where I need it most and I can still run my target VMs.
For me Windows is disqualified from the start because it's not Unix or Plan 9. The nature of my work requires a Unix environment, and even if it weren't the case, I'd still prefer a Unix/Plan 9 environment.
The various Unix emulation layers available in Windows like Cygwin, SFU/SUA/Interix, UWIN, MKS don't satisfy me the slightest, and even if they did, they'd restrict me to the Unix side of things while on Linux or Mac OS X I most often use plan9port.