WP_Query on custom taxonomy works fine but fails in wp_ajax_

<?php
/* the class file mentioned on http://wordpress.stackexchange.com/questions/32088/wp-query-on-custom-taxonomy-works-fine-but-fails-if-run-through-wp-ajax */

$jttvvs = new jttv_ViewStats();

class jttv_ViewStats {

    function __construct()
    {
        add_action( 'admin_menu', array( $this, 'jttvvs_admin_menu') );
        add_action('wp_ajax_get_views', array( $this, 'get_views') );
    }

    /**
     * Add the admin page
     */
    function jttvvs_admin_menu()
    {
        $page = add_submenu_page('jimmyteenstv', __('View Stats'), __('View Stats'), 'edit_themes', 'jttv_viewstats', array( $this, 'jttvvs_settings_page') );
        add_action("admin_print_scripts-$page", array( $this, 'jttvvs_js') );
        add_action("admin_print_scripts-$page", array( $this, 'jttvvs_css') );
    }

    /**
     * load the js
     */
    function jttvvs_js()
    {
      wp_enqueue_script( "jttv_viewstats", WP_PLUGIN_URL .  "/stats/js/jttv_viewstats.js", array( 'jquery' ) );
    }

    /**
     * load css
     */
    function jttvvs_css()
    {
    ?>
<style type="text/css">span.loader { background: transparent url( WP_PLUGIN_URL .  "/stats/assets/loader.gif") no-repeat 0 0; width:16px; height:11px; display: block; margin:3px 0 0 15px;}</style>
    <?php
    }

    /**
     * ajax return
     */
    function get_views()
    {
        $args = array(
            'posts_per_page'=> -1,
            'post_status' => 'publish'
        );

        if ( isset($_POST['tag_id']) ) :
            $args['tax_query'] =
                array(array(
                    'taxonomy' => 'region',
                    'field' => 'id',
                    'terms' => $_POST['tax_id'],
                ));
        endif;

//echo '<pre>' . print_r($args, true) . '</pre>';

        $the_query = new WP_Query($args);

        while ( $the_query->have_posts() ) : $the_query->the_post();

            $reg = get_post_meta(get_the_ID(), 'reg_count');
            $unreg = get_post_meta(get_the_ID(), 'unreg_count');
            $reg_count = $reg_count + $reg[0];
            $unreg_count = $unreg_count + $unreg[0];
        endwhile;

        echo "total: " . number_format($reg_count + $unreg_count);

        die();
    }

    /**
     * non ajax return
     */
    function get_views_nojax($tax_id = false)
    {
        $args = array(
            'numberposts' => -1,
            'post_status' => 'publish'
        );
        if ( isset($tax_id) ) :
            $args['tax_query'] =
                array(
                    array(
                        'taxonomy' => 'region',
                        'field' => 'id',
                        'terms' => $tax_id
                );

        endif;

        $posts = get_posts( $args );

        foreach ( $posts as $post ) :

            $reg = get_post_meta($post->ID, 'reg_count');
            $unreg = get_post_meta($post->ID, 'unreg_count');
            $reg_count = $reg_count + $reg[0];
            $unreg_count = $unreg_count + $unreg[0];

        endforeach;

        return "total " . number_format($reg_count + $unreg_count);
    }

    /**
     * the regions
     */
    function list_regions()
    {
        // regions
        $args = array(
            'orderby' => 'name',
            'order' => 'ASC',
            'taxonomy' => 'region',
            'child_of' => 0
        );

        $cats = get_categories($args);

        foreach ( $cats as $cat ) :

            echo '<tr>';
                echo '<td>' . $cat->cat_ID . " " . $cat->name . '</td>';
                echo '<td id="' . $cat->cat_ID . '">' . $this->get_views_nojax($cat->cat_ID) . '</td>';
                echo '<td id="' . $cat->cat_ID . '"><a class="button-secondary getviews">Count Views</a></td>';
            echo '</tr>';

        endforeach;
    }

    /**
     * Create the viewable page
     */
    function jttvvs_settings_page()
    {
    ?>
        <div class="wrap">

            <div id="icon-options-general" class="icon32"></div><h2>Film View Stats</h2>
            <table class="widefat">
            <tr>
                <td>Total Views:</td>
                <td><?php echo $this->get_views_nojax($cat->cat_ID); ?></td>
                <td width="50%"><a class="button-secondary getviews">Count Views</a></td>
            </tr>
            <tr>
                <td colspan="3">&nbsp;</td>
            </tr>
            <?php $this->list_regions(); ?>
            </table>

        </div>

    <?php
    }

}//


?>

/* the jquery - in a separate file - loaded through function jttvvs_js() */
jQuery(document).ready( function($) {
    $("a.getviews").click( function() {
        var td = $(this).parent();

        /* only fetch results once */
        $(this).unbind('click').bind('click', function(){return false;});

        // replace button with loader
        $(td).html('<span class="loader"></span>');

        $.post($(this), {
                action: "get_views",
                tax_id: td.attr("id")
            }, function(data) {
                td.html(data);
            }
        );
        return false;
    });
});