Actually IMO majority of hacker news commenters are left leaning, and I try avoiding political news here because their rethoric is tiring (to me).
I notice that the comments usually the fit the article. For example, this has tons of comments sympathetic to Stallman (he's generally pro-socialist). While some other pro-libertarian article would have mostly comments sympathetic to capitalism, libertarian, etc. This occurs on Reddit too.
So libertarian/pro-capitalist people see HN as left-leaning, while left-leaning people see HN as pro-capitalist.
If HN is seen as left-leaning, then the political diversity spectrum in the US is in truly dire shape.