Don't forget, because $_REQUEST is a different variable than $_GET and $_POST, it is treated as such in PHP -- modifying $_GET or $_POST elements at runtime will not affect the ellements in $_REQUEST, nor vice versa.
$_GET['foo'] = 'a';
$_POST['bar'] = 'b';
var_dump($_GET); // Element 'foo' is string(1) "a"
var_dump($_POST); // Element 'bar' is string(1) "b"
var_dump($_REQUEST); // Does not contain elements 'foo' or 'bar'
If you want to evaluate $_GET and $_POST variables by a single token without including $_COOKIE in the mix, use $_SERVER['REQUEST_METHOD'] to identify the method used and set up a switch block accordingly, e.g:
case 'GET': $the_request = &$_GET; break;
case 'POST': $the_request = &$_POST; break;
. // Etc.