It is not just lazy, unwatchfull Bloggers with undertrafficed sites that get the comment “manipulators”..
A technorati search for Comment Spam will yield a constant flow of posts posted by bloggers from all across the web.
The comment spammers bring down servers on the level of a Dos attack such is the volume.
I tried to implement a blog, and within days it was being hit by the same type of proxies (proxys?) as technorati mentions. Also, a lot of the newer type blog scripts allow mobile phone commenting, whereas you don’t even have to be on the computer to dole out 200 messages in 2 minutes. Needless to say, I permanently shut the blog down, it wasn’t worth it,as it was not being productive with ‘comment spammers’ strangling the would be life out of it. And yes, this type of comment spam could overload your server and become as DOS-like attack.