Windows is inherently high maintenance in my experience unless you keep your installed applications to a very specific short list. Uninstalling software, or worse, drivers, can be an exercise in frustration.
I've never had an issue removing software on OS X as applications are generally quite well behaved or they're effectively managed by the Darwin Ports system.
It's also great that doing source installs on OS X is trivial. I don't think the same can be said for Windows. Tradition is to go the binary installer route there, and there's so many badly written installers.
While I respect those that choose to use a Linux-based desktop, as it can be quite a chore to keep up to date and tricky to get different apps to work together politely, I'd say that approach only works for people with intimate familiarity with the various quirks and caveats of their distribution. To get something like Debian, Ubuntu or Gentoo running in top form takes talent.
Making Windows into a productive development environment can be just as much of a challenge, too, and there's some things that can never change. The registry is a persistent horror, drive letters and backslashes in paths are an extreme nuisance, and the second-class status of things like a proper command line shell and compiler are just examples of my grievances with Windows.
While it's possible to glue together a workable environment in Windows, especially if it's just for something simple like PHP + MySQL, once you really want to stretch your legs and be more adventuresome you may run into trouble.
Although it could be fanboyism, 99% of the people I see at web-biased conferences are on Mac machines. It's the singular dude using the Dell who's doing the "think different" thing.