Testing plugins on Windows IIS server, necessary???

Is it necessary to test plugins on a server running Windows IIS? I have no idea what percentage of wordpress sites are running on Windows servers, but it can be done. And when plugins are available to the general public, there is no way to know what operating system will be running on the server. If you don’t use things like the DIRECTORY_SEPARATOR constant, then certain things that work perfectly on Linux might not work at all on Windows. People have also told me that some of the $_SERVER variables are different. I do all of my development and testing on Ubuntu. But I was wondering if there might be enough wordpress sites out there running Windows that I should test them on servers running Windows and IIS before making them available to the public. Any opinions on that would be interesting to hear.