According to that article LiveJournal was (is?) overwriting existing affiliate links with their own. According to their co-founder, Posterous is only affiliating links that aren't already affiliated (ref: http://news.ycombinator.com/item?id=1309604).
Well, from what I remember in followup coverage, lj claimed that overwriting existing affiliate links was a bug, and they were also just trying to affiliate links that aren't already affiliated.
http://www.techdirt.com/articles/20100304/1741458425.shtml