Well here's an interesting observation: the "right" subreddit cites some sources that the "left" subreddit cites, but not vice versa. For example, NYT and Politico appear near the tail of the "right" sub's sources and near the head of the "left" sub's sources, but none of the "right" sub's sources appear anywhere in the "left" sub's sources.
So, assuming that NYT and Politico are left-leaning, it would appear that the "right" sub links to its opponents' views, while the "left" sub does not.
The conservative subreddit links to archive.us (notice it is 2nd on the list) instead of the NYT, WaPo, etc. because they do not want those news orgs to capitalize from traffic it would be sending there; instead they send their massive conservative user base to archive. (i suppose this behavior might be another interesting observation?)
This is not just because of traffic, but to get the original story. There have been plenty of times where the story was changed and edited after the initial post.
So, assuming that NYT and Politico are left-leaning, it would appear that the "right" sub links to its opponents' views, while the "left" sub does not.
The implications of this are left to the reader.