Ask HN: Purpose of email address in blogs' comment box?

WordPress blogs (and some other websites) require email addresses. The email addresses are only used for sending notification of replies, isn't it? (or a kind of CAPTCHA). Some people are reluctant to type their real email or just give up leaving a comment. The owners may miss some opinions from those people then. Sample page: http://wpthemetutorial.com/2013/05/02/working-with-vagrant-and-wordpress-basics/