It may be that allyson hannigan wears the same outfit for a whole season because the producers use a bit of slight of hand and combine episodes out of order to keep them fairly interesting.
penn and teller likelwise wear the same outfit for a whole season.
i could be wrong.
but look at the audience behind penn and teller. they will sometimes change like magic to appear to be different people, mid episode.
i love it when someone fools them and the huge trophy comes down with the F U
