I'm not sure what is happened but a few things:
1. i am using WP-MAIL-SMTP plug in
without this the admin does not receive email since the server/php is not configured.
2. when activated, the email set in the plug in receives an email, however the user email does not.
I also wrote in the following (cut out some of the code) into a custom plug in and neither sends an email:
wp_mail($user_email, sprintf(__('[%s] Your username and password'), $blogname), $message);
wp_new_user_notification($user_register,null,'both');
3. note that when i reset a users password that user will receive an email notifying them