Why do people that comment don't have a link to unsubscribe?

Today some people that commented one of my images asked me how to stop receiving e-mails from skitch, notifying about new comments.
I told them that should be a link to unsubscribe on the e-mail received, but this isn't true. They just have a little text, with a link to the page.

This is a huge problem. They SHOULD be able to unsubscribe.