It's the question of reusability of software. I know about people (including myself) who wrote stuff running on Windows. And they did not write it on Linux just because either they didn't need it or simply because they don't understand Linux programming that much or even not at all. Now, does that mean we should throw away all the stuff which has been done? It's unlikely to happen those users will port it on Linux. So the question is,
Then ask for help!
What is there that can only be done on Windows but not on Linux? No examples have been presented yet.
If it just boils down to "I feel cozy using C# on windows and never had a look at mono", then I'm sorry, that doesn't cut it for me. I had to acquire a considerable amount of expertise and put in a substantial amount of time to do the stuff I'm doing on the toolserver. Shelling out even one dollar just because someone is to lazy (sorry) to learn new things seems unacceptable to me.