login versus provide email

I am a newbie. I have set these Discussion Options: Allow people to post comments, E-mail me whenever a comment is held for moderation, Before a comment appears, An Administrator must approve the comment, and Comment Author must fill out name and e-mail.

When a reader sees the site, she gets the message “You must be logged in to post a comment” and the words logged in link her to a screen asking her to supply username and password. She is not given an opportunity to provide email and register, and submit a comment for moderation. Why is this?