Sure nobody is really running any PHP sites on Windows boxes, but they're sure as hell developing on them. And while I get that the core PHP devs couldn't find a Windows machine if their lives depended on it, enabling coders on Windows machines is what brought them to their current size - something they've clearly forgot since http://pecl4win.php.net/ died.[/endrant]
VMWare Player and VirtualBox are free, and it's quite easy to setup an Ubuntu image that mimics your server platform (if you must be untethered)... alternatively put everything in the (private, if need be) cloud.
I am perfectly happy with this setup, and haven't run across any downsides.
Developers appreciated that significant config changes boiled down to: get all of your local changes into version control, then grab the newest VM image off the network drive.
It's significantly more painful when you get out of that environment. If you have lots of projects, juggling VMs is a pain. They take up lots of space. Spinning them up/down takes minutes. You don't just have one working IP/hostname/Samba mount/etc that's always there. The resource hit from running a VM is a bigger deal on a netbook. Etc..
For my own projects, I would rather work in Windows, with a mild annoyance when testing, than consistently be annoyed by working in either. (I do use a VM for testing before pushing to production, but for quick "is this right" testing, bouncing Django on Windows and eyeballing it is generally good enough to keep pushing forward.)
You can still develop on Windows, just instead of testing on localhost, you'd test on local VM.
Hell, that's what I do and my main Desktop does run Linux, but I devel on a junk machine running Apache/PHP, PostgreSQL.
First part is somewhat false. Second part is very true.
Having developed, provided, and commercialized a WAMP server that was started in 2003 (http://www.devside.net/server/webdeveloper) I've gain some knowledge of who uses PHP on Windows.
Everyone. In all kinds of situations. There is absolutely nothing lost between hosting Wordpress on Windows vs. Linux. Security, performance, maintainability, etc.
I've also found that around 2009, half of the Apache, MySQL, and PHP downloads from their official sites where for the Windows builds.
These numbers have only gone up since then.
The Windows platform for PHP is critical to the health of PHP. Loose it, and you've lost half of the developers and about 30% of the production deployments.