It is easier for a user to scroll down a long continuous list than to hop back and forth between two columns. This is particularly true for ordered lists (as is the case with HN).
The only thing I strongly dislike about HN's current design is that comment line lengths are far too long[1].
The only thing I strongly dislike about HN's current design is that comment line lengths are far too long[1].
[1] http://baymard.com/blog/line-length-readability