I suppose that I'm assuming some kind of proprotionality in upvoting or downvoting, maybe even two varieties of proportionality.

First, I'm assuming that Windows-users are represented proportionally with the general population in the Hacker News population.

Second, I'm assuming that Windows-users and Linux-users would be equally inclined to up- or down-vote any given story. That is, the proportion of voters (your "small minority" that votes) is the same in Windows-users population and Linux-users population.

Your point about Haters vs Haters-fighters is well taken.