I've recently picked up over 2000 spam comments. The comments are of the trackback variety in the related blogs area of robo blog sites. So the reason in my case would be a high rating for the type of search used by the plug in they are using. Many times it is a search for a adjective - in this latest round I am guessing the word was "width"
Being scrapped may not be a bad thing in small numbers as it keeps a site appearing but I worry about high numbers. As to many may reflect badly on the site even though it should not.
Akismet also helpped me clean up the mess - had to hit "check for spam" on the bottom of the comments page. Thank you Akismet without which I would no longer be able to use comments if somebody wanted to comment.