it does work, BUT it may be:
1. disabled (allow_url_fopen "0" in php ini)
2. you may get the html output only from the other site if it has php enabled and has executed your script..
i dont know why you'd want to fpassthru a php script ? because fpassthru does not execute any opened php code, it only shows it, therefor it wouldn't matter if the other site showed you the php code anyway..