pg_shadow / pg_user

Hi friends,

I've been learning about security using Pg lately.
Up until last night I thought system user passwords were stored safely away in pg_user.
So far I haven't been able to get any passwords out only '*******'.
Then last night was observing each system table and found that pg_shadow stores user passwords in clear text.
??
pg_shadow = clear text password
pg_user = hidden password

I guess this means if an intruder gets an appropriate account on the box the can view all passwords.
I had assumed that system passwords were stored hidden from all eye balls.
Sort of like apache storing http passwords in binary form in a db.

Is this how it is ?

If so I was thinking I like to know if someone tries or succeeds in querying the pg_shadow table.
I thought maybe to increase the postmaster debug level so that all sql queries are logged.
Then write a cron job to check this log and email me if it is detected that a user is attempted or did query
the pg_shadow table.

How does this sound ?
Am I totaly on track ?

Thank for your time and attention
Kind regards
Rudi.