Select in subselect vs select = any array

I have noticed that SELECT ... = ANY(ARRAY(...))  is about twice as fast as SELECT IN ( ... ).
Can anyone explain a reason for this?  Results are the bottom and are reproducible.  I can test with other versions if
thatis necessary. 

./configure --prefix=/usr/local/pgsql84 --with-openssl --with-perl
CentOS release 5.4 (Final)
psql (PostgreSQL) 8.4.1

prompt2=# select count(*) from nodes;
 count
--------
 754734
(1 row)


prompt2=# \d nodes
                                        Table "public.nodes"
    Column    |           Type           |                         Modifiers
--------------+--------------------------+-----------------------------------------------------------
 node_id      | integer                  | not null default nextval(('node_id_seq'::text)::regclass)
 node_type_id | integer                  | not null
 template_id  | integer                  | not null
 timestamp    | timestamp with time zone | default ('now'::text)::timestamp(6) with time zone
Indexes:
    "nodes_pkey" PRIMARY KEY, btree (node_id)
    "n_node_id_index" btree (node_id)
    "n_node_type_id_index" btree (node_type_id)
    "n_template_id_index" btree (template_id)

prompt2=# select count(*) from nodes where node_id = any(  Array(select node_id from nodes limit 100000) );
 count
--------
 100000
(1 row)

Time: 404.530 ms
prompt2=# select count(*) from nodes where node_id = any(  Array(select node_id from nodes limit 100000) );
 count
--------
 100000
(1 row)

Time: 407.316 ms
prompt2=# select count(*) from nodes where node_id = any(  Array(select node_id from nodes limit 100000) );
 count
--------
 100000
(1 row)

Time: 408.728 ms
prompt2=# select count(*) from nodes where node_id in (select node_id from nodes limit 100000 );
 count
--------
 100000
(1 row)

Time: 793.840 ms
prompt2=# select count(*) from nodes where node_id in (select node_id from nodes limit 100000 );
 count
--------
 100000
(1 row)

Time: 779.137 ms
prompt2=# select count(*) from nodes where node_id in (select node_id from nodes limit 100000 );
 count
--------
 100000
(1 row)

Time: 781.820 ms