unregister_widget() not working for some widgets

I’m using the following code in functions.php to turn off a number of default widgets so that they do not appear in the admin tools:

function unregister_default_wp_widgets() {

	unregister_widget('WP_Widget_Pages');

	unregister_widget('WP_Widget_Calendar');

	unregister_widget('WP_Widget_Archives');

	unregister_widget('WP_Widget_Links');

	unregister_widget('WP_Widget_Meta');

	unregister_widget('WP_Widget_Search');

	unregister_widget('WP_Widget_Categories');

	unregister_widget('WP_Widget_Recent_Comments');

	unregister_widget('WP_Widget_RSS');

	unregister_widget('WP_Widget_Tag_Cloud');
}

add_action('widgets_init', 'unregister_default_wp_widgets', 1);

The problem I’m running into is that it is removing some widgets, but not others … namely, “Search” and “Meta,” which still appear on the Widgets page. Anyone know why?