Drop user doesn't drop granted privs?

Correct me if I'm wrong, but it seems that PostgreSQL 7.4 does not remove a user's privileges on tables when that user is dropped.  The privileges are still showing up if I do a \z in psql, but with the SYSID instead of the username (obviously, since the username doesn't exist.)  Is there an easy way to remove the privileges, either at the same time a user is dropped, or afterwards?

Pete