Exclude child comments in get_comments() or WP_Comment_Query?

This should do the trick, I guess:

$args = array(
    'number'      => 10,
    'order'       => 'DESC',
    'status'      => 'approve',
    'parent'      => 0
);

$comments = get_comments( $args );

You can find full list of arguments in Codex.