superuser unable to modify settings of a system table

On PG 8.4.4 I am unable to set per-table autovacuum setting for the
pg_listener table. Being a superuser, I'd expect Postgres to allow me to do
that.

postgres=# select version();

version
-----------------------------------------------------------------------------------------------------------
 PostgreSQL 8.4.4 on i686-pc-linux-gnu, compiled by GCC gcc (GCC) 4.3.2
20081105 (Red Hat 4.3.2-7), 32-bit
(1 row)

postgres=# select user;
 current_user
--------------
 postgres
(1 row)

postgres=# alter table pg_listener set (autovacuum_vacuum_threshold=100);
ERROR:  permission denied: "pg_listener" is a system catalog
postgres=# select * from pg_user;
 usename  | usesysid | usecreatedb | usesuper | usecatupd |  passwd  |
valuntil | useconfig
----------+----------+-------------+----------+-----------+----------+----------+-----------
 postgres |       10 | t           | t        | t         | ********
|          |
(1 row)

Regards,
PS: RhodiumToad prompted me to post here.
--
gurjeet.singh
@ EnterpriseDB - The Enterprise Postgres Company
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