There is a technology called Auto Unsubscribe that is supported by some email companies like MailChimp and others. Google now unsubscribes you when an email that supports this is marked as spam.
http://gmailblog.blogspot.com/2009/07/unsubscribing-made-easy.html
Is there a plugin for Apple Mail or could this maybe, perhaps, be added to a future SpamSieve release? This would help lessen the spam because a few of the emails might be from legit companies and the users, like me, might have forgotten they subscribed to the list.