What does count(*) count?

Hi all,
I tried to dump out a single table and just for a verification I counted the
number of 'INERT INTO' rows.
I found that count(*) results less rows than grep.
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Csaba@compaq ~
$ pg_dump -d -t t_stockchanges alumil6 > sc.dump

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alumil6=# select count(*) from t_stockchanges ;
 count
-------
  9816
(1 row)

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Csaba@compaq ~
$ cat sc.dump | grep 'INSERT INTO' | wc -l
   4908

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What can be the reason of it?

Thx,

-- Csaba