Have the posts gotten longer, or are more people including "longer signatures" on their posts? Is there a way to compare the "uniqueness" of each post?
I think you should exclude accounts that are aggregating the work of others, as well as those that appear to me automated, curation programs that summarise their votes. I don't believe these are genuine "content" in the way that an individual author may compose.
Some other have suggested this, and the bilingual posts as well..... probably has some effects