Anybody that has a website that permits both comments and search engine spiders has run into comment spammers. They don’t care about rel=”nofollow” attributes. They don’t care about the subject matter of your site. They just post their gibberish and URLs and get out of dodge. One of the mechanisms I use to reduce the amount of comment spam on the sites I maintain is Akismet, who have been kind enough to publish stats on the sheer volume of garbage being dumped onto our Internets these days (which, contrary to popular belief, is much like a dumptruck: you can pile all kinds of stuff onto it).
Their stats map pretty nicely to the raw volume of unsolicited bulk email that my benevolent employer sees. It’s nice to know that the spammers are keeping their minds open to both new and old vectors to defraud the public.