Spammers must be dumb

Man, those comment spammers are relentless. All month I've been logging 404 errors from comment spammers with spammy referrer URLs trying to hit my MT installation. If they were actually hitting the scripts (a few are), I might be really annoyed. But the fact that they're all going to a bad URL and just getting 404 pages only has me mildly annoyed at the moment. What's more puzzling is that none of the spammy referrer URLs are even real. So what are these guys tring to point people to? And if they keep getting 404 errors, why do they keep trying? These guys are either incredibly stupid or their spambots are incredibly stupid. Or more likely both.