[laumars]

I think it's a bit of a stretch to say the opening credits are "always a bit different". I can think of quite a few shows display the episode directors and any guest stars after the intro (ie during the first scene of the main episode). I presume they do this to save editing time and cost changing the intro - though there's also the convenient side effect of still having the credited names appear on screen even when viewers fast-forward through the intro.