empty pg_stat user views

On Posgresql 8.1, debian

I have turned on stats collection:

stats_start_collector = on
stats_command_string = on
stats_block_level = on
stats_row_level = on
stats_reset_on_server_start = on

and am collecting system stats (eg. pg_statio_sys_tables).  This is
great.
  select count(*) from pg_statio_sys_tables;
returns 52 rows

However, all my user views are empty (eg. pg_statio_user_tables).
    select count(*) from pg_statio_user_tables;
returns 0 rows

Could someone explain this?

Thank you,
Bob