For reasons I don't really understand, the body first function was causing a parse error. I split up the test and everything is fine now (see the new code for the function below). With this fix, the plugin does exactly what I want -- hopefully Jaka can update the plugin (maybe it is a WP2.7.1 issue?) so others can take advantage of it too.
Thanks!!
function ncop_comments_open_filter($open, $post_id=null)
{
if($open) {
$post = get_post($post_id);
if($post->post_type !== 'page') {
return true;
}
}
return false;
}