Actually, the document the White House released last week is titled "CERTIFICATE of Live Birth," not "Certification." Regardless, it was most likely phony, and Obama's lawyers would have been foolish to even mention it.
Lack of "Standing" is a much more convenient way for them to argue for the lower court's decision. For the judiciary, lack of "standing" is a convenient game to play as well, because it insulates Obama from any court decision on the constitutional eligibilty issue on its merits.