Actually the comment spam you’re seeing is from k5’s Group A.
Group B wants you to visit their site, so they try to trick you into clicking through by pretending to be relevant information. Group A just wants PageRank, so they do their best to make sure the link gets followed by Google.
The reason you’re seeing the spam is because you’ve subscribed to my comment feed. Bloglines checks my site while I’m asleep, when I wake up the first thing I do is despam my blog. Google probably checks my site too overnight, which means that these comment spammers were getting indexed as links from me for a few hours, and so they had incentive to post to my site.
With nofollow they’ve now lost those few hours because their links aren’t indexed even if they make it past MT-Blacklist.