I disagree. Those are real people who do that kind of work. When I was looking for online work at sites like getafreelancer or rentacoder there usually were tons of job offers regarding forum posts/blog comments. Rarely labeled as forum/blog spam but often meaning that. Here's a typical (current) job offer for forum posts: http://is.gd/c3dIo (This is not intended as advertising but only to provide an impression of such a job offer and as evidence that such job offers actually do exist and are common, depending on where you look.)
In this particular job, they offer $20 for 400 posts (or 2000 replies). Most often, one condition of posting such stuff is that it is at least unique, "original work" or would "pass copyscape".
So, there seem to be people who actually do this kind of job manually.
Exactly, real people are hired to generate backlinks via blog comments. I consider it spam, but since the goal is to make a relevant comment, that's debatable. The example given in this post however, is automated. You don't hire people to write unique content and have them list keywords. That's the type of spam I'm referring to as automated.
In this particular job, they offer $20 for 400 posts (or 2000 replies). Most often, one condition of posting such stuff is that it is at least unique, "original work" or would "pass copyscape".
So, there seem to be people who actually do this kind of job manually.