I was just thinking on this.

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.