Why can not we get PHP form variables？

If we use PHP4.2 version or above, click here.
Set register_globals = on or
By adding the following code:
// allow script to work with registerglobals off
if ( function_exists('ini_get') ) {
$onoff = ini_get('register_globals');
} else {
$onoff = get_cfg_var('register_globals');
}
if ($onoff != 1) {
@extract($HTTP_SERVER_VARS, EXTR_SKIP);
@extract($HTTP_COOKIE_VARS, EXTR_SKIP);
@extract($HTTP_POST_FILES, EXTR_SKIP);
@extract($HTTP_POST_VARS, EXTR_SKIP);
@extract($HTTP_GET_VARS, EXTR_SKIP);
@extract($HTTP_ENV_VARS, EXTR_SKIP);
}
TITLE: Why can not we get PHP form variables？