I never understood why people use the same exact email address to sign up for multiple sites. Any decent MTA will give you a wildcard extension on your username, so signing up for service Foo means telling them something like user-foo@example.com. An unsubscribe is as simple as forwarding that specific address to bounce, /dev/null, or their whois contact information (although I generally reserve that last one for articles that pop up a subscribe box when viewing). This also gives you the advantage of seeing who has sold your email address.
Seeing which email addresses leak is just an interesting reflection on the company. For example, the supposedly non-visible address I gave to facebook gets spam.