extract(timezone_hour) problem

I understand that internally, Postgres converts timestamps to a GMT format
and then redisplays them in the local timezone. cf:
http://groups.google.com/groups?selm=Pine.LNX.4.30.0110100104320.672-100000%40peter.localdomain&oe=UTF-8&output=gplain

However --> doesn't this make the extract(timezone_hour...) function
basically useless? May as well call it "get_local_timezone_hour". How can
one extract the timezone offset of a timestamp w/timezone (ie. get the
intended behaviour of the extract call) ???

blackcherry=# SELECT extract(timezone_hour from TIMESTAMP WITH TIME ZONE
'2001-02-16 20:38:40-05');
date_part
-----------
8
(1 row)

blackcherry=# SELECT extract(timezone_hour from TIMESTAMP WITH TIME ZONE
'2001-02-16 20:38:40-00');
date_part
-----------
8
(1 row)

-Dave

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