Probably so. Though I would suggest that the neither one is a small niche in itself. Mac especially--it's the favored platform for every developer I know except one. Yes, it's less popular outside tech circles (probably due in part to the price).
Imagine this scenario: There are tons of Mac users who want to learn Haskell. They try it, but can't install libraries. The Haskell community never hears from them; one could say the system failed silently. Meanwhile, Linux works fine, and the Haskell-Linux community keeps growing.
So perhaps there's a self-reinforcing Linux-centric bias in the developer population.