In case of long emails this link might be easy to miss or the recipient just won't bother looking and will pick the easiest way to get rid of your emails - mark it as a SPAM. This will solve the "problem" for the recipient but will hurt you.
Guys at Gmail know this so they decided to make it easier to unsubscribe. From now on all the emails with an active unsubscribe option in the Social, Discussions boards and Promo tabs will have the unsubscribe button displayed in the header next to the sender address. Your recipients simply won't be able to miss it.
This new visibility for the unsubscribe button is good for everyone. Recipients will save time looking for the right button to unsubscribe and reduce the number of emails reported as SPAM as a result of time-saving instead of using the unsubscribe.