Spammers must be stupid...
... or, at least, have too much time to waste.
They don't even bother reading notices and keep trying to post comments that will never be published.
Like someone here could be interested in their thesis-writing-services: if they can't read, why should I give 'em money to write?
Maybe I'll start asking a valid mail address (to validate entering a code) to who tries to post a comment. And if the comment is spammy, the address (not the spammy comment) will be published for other spammers to harvest and fill with viagra/cialis/etc offers -- so they'll have something better to do other than posting spam here. Don't you think that could be an useful service?