Is there ever a good reason as to why you, email sender, might want to include an unsubscribe link in your transactional email messages? Why yes, yes there is. This isn't the first time I've seen somebody have to resort to publicly crying "uncle" due to the deluge of misdirected transactional notifications.
July 30, 2012 edit: Here's another example of a misdirected transactional email message causing some recipient grief. It's sad to see the retailer can't do more to make this stop.