Mistery about commit statement

hi!

I read a lot regarding commit enhacements in 10g and also 11g and everything seems clear to me. But on my databases I can't understand the results of this test script, where I compare the different types of commit:

/*
CREATE TABLE COMMIT_TEST
(
  ID           NUMBER(10),
  DESCRIPTION  VARCHAR2(50 CHAR)
)
TABLESPACE USERS
NOCOMPRESS ;

CREATE UNIQUE INDEX COMMIT_TEST_PK ON COMMIT_TEST
(ID)
TABLESPACE USERS;

ALTER TABLE COMMIT_TEST ADD (
  CONSTRAINT COMMIT_TEST_PK
  PRIMARY KEY
  (ID)
  USING INDEX COMMIT_TEST_PK
  ENABLE VALIDATE);
*/

SET SERVEROUTPUT ON

DECLARE
  PROCEDURE do_loop (p_type  IN  VARCHAR2) AS
    l_start  NUMBER;
    l_loops  NUMBER := 2000;