The checkbox will appear wherever the do_action(‘comment_form’,$post->ID); command in their themes comments.php . It is that command that tells WordPress plugins that the comment form is being rendered to the page and any plugins that want to add something to the form should do it now. If they want to move it, they need to edit their comments.php file and move that command (it should not be outside the <form> </form> tags and needs to be enclosed in <?php ?> tags if it isn’t already part of some php block)
I am thinking of moving the code on Technology Bloggers, and thought that others may be looking to do the same!
Answer found here: http://growmap.com/growmap-anti-spambot-plugin/
Hope this helps :-)