RTREE Index on primary key generated by a sequence

Hi all,

Since I was at first Oracle DBA, I've been told many times at
professional trainings that when there is a table wich primary key is
generated by a sequence, it is worth create a RTREE index on it rather
than a BTREE (for index balancing reasons).

But, I wanted to try it with my PostgreSQL 7.1.3 and:

---
contacts=# \d t_contact
Table "t_contact"
Attribute | Type |
Modifier
-------------------+------------------------+--------------------------------------------------
cnt_id | integer | not null default nextval('contact_id_seq'::text)

[snipped all other columns...]

contacts=# drop index t_contacts_pkey;
DROP

contacts=# create unique index t_contacts_pkey on t_contact using rtree
(cnt_id);
ERROR: DefineIndex: unique indices are only available with the btree
access method

contacts=# create index t_contacts_pkey on t_contact using rtree
(cnt_id);
ERROR: DefineIndex: opclass "int4_ops" not supported by access method
"rtree"
---

So I think there are 2 possible reasons:

1) PostgreSQL has strong algorithms to manage indexes greatly, avoiding
this kind of BTREE index being unbalanced time passing ( I mean a kind
of automatic detection of unbalanced BTREE => triggers a DROP and CREATE
index...)

2) It is not yet implemented and you want to do it for the next version
:)

Whih of 1) & 2) is true?

Where to find more information about index management in PostgreSQL?

Thanks a lot.

--
Jean-Paul ARGUDO IDEALX S.A.S
Consultant bases de données 15-17, av. de Ségur
http://IDEALX.com/ F-75007 PARIS