I won't go into details in deference to those who think Al Qaida get all their information here, but it took me all of one second to figure out a way round this 'defence'. I expect any cogent hijacker could do the same.
Hard to see this being anything other than window-dressing, a way of reassuring the US public (well, those on the ground anyway). If it really is an integral part of the strategy, then why on earth publicise it ?
OTOH, Uhlman's Razor may well apply.