+1 to this. The friction of finding, setting up, and using Windows isn't even comparable to just sshing into another unix box and testing something quickly.
As a university student, I also find it relatively rare that I get to test on a Windows machine. My personal computer runs linux, my technical friends run linux or osx, and my non-technical ones run osx. Also, all the school servers that I have access to run either FreeBSD or Linux.
If I want to run something on linux system, I have about 40 different computers that I can ssh into and run code on.
If I want to run something on osx, I just have to call a friend and ask if they can turn on their computer and allow me to ssh in (to my own account, of course).
If I want to run something on Windows, I have to track down a friend (in person!), ask to borrow their computer for a few hours, get administrator access to install the Haskell Platform, get frustrated that HP hasn't been upgraded to 7.6, and give up.
It's just not practical, especially for the large amount of small (<500 LOC) packages on Hackage.
- Clark