SQL Server UPDATE much faster than Oracle -- why??

Question

The following MS-SQL Server (2000) UPDATE takes 10 seconds, while the same Oracle 10.2.0.1 UPDATE takes over 15 minutes. The data is exactly the same (data set of 97,000 rows) and the cpu/disk/memory configs are similar for both databases. The Oracle tables have indexes and statistics gathered. The Oracle Explain Plan shows that indexes are being used for the SELECT table joins, but not for the UPDATE table.
Any ideas?
MS-SQL UPDATE:
update lib_cust_summary
set rev_2003 =
SELECT
sum(ohd.PRICE_EXTENSION)
FROM
oehist_summary ohs
,customers c
,oehist_detail ohd
,lib_cust_summary lcs
WHERE c.cust_nbr     = lcs.cust_nbr
and c.cust_nbr = ohs.cust_nbr
and ohs.INVOICE_NBR = ohd.INVOICE_NBR
and c.cust_nbr = lcs2.cust_nbr
and ohs.CUST_NBR NOT LIKE 'XFER%'
and     ohd.prod_grp not in ('AV','FE')
AND ohs.INVOICE_DATE between {ts '2003-01-01 00:00:00'} and {ts '2003-12-31 00:00:00'}
group by c.cust_nbr
from lib_cust_summary lcs2;
Oracle UPDATE
update lib_cust_summary lcs /*+ index(lcs lib_cust_summary_pk) */
set rev_2003 =
SELECT /*+ index(lcs lib_cust_summary_pk) */
sum(ohd.PRICE_EXTENSION)
FROM
oehist_summary ohs
,customers c
,oehist_detail ohd
WHERE c.cust_nbr = lcs.cust_nbr
and c.cust_nbr = ohs.cust_nbr
and ohs.INVOICE_NBR = ohd.INVOICE_NBR
and ohs.CUST_NBR NOT LIKE 'XFER%'
and     ohd.prod_grp not in ('AV','FE')
AND ohs.INVOICE_DATE between '01-JAN-2003' and '31-DEC-2003'
group by c.cust_nbr
)

Answer 1

update lib_cust_summary lcs /*+ index(lcs
s lib_cust_summary_pk) */
set rev_2003 =Why are you forcing the optimizer to read a full table by using an index?
SELECT /*+ index(lcs lib_cust_summary_pk) */What happens if you remove this hint also?
sum(ohd.PRICE_EXTENSION)
FROM
oehist_summary ohs
,customers c
,oehist_detail ohd
WHERE c.cust_nbr = lcs.cust_nbr
and c.cust_nbr = ohs.cust_nbr
and ohs.INVOICE_NBR = ohd.INVOICE_NBR
and ohs.CUST_NBR NOT LIKE 'XFER%'
and     ohd.prod_grp not in ('AV','FE')
AND ohs.INVOICE_DATE between '01-JAN-2003' and
d '31-DEC-2003'You should not compare dates to strings
AND ohs.INVOICE_DATE between to_date('01-JAN-2003','DD-MON-YYYY') and
to_date('31-DEC-2003','DD-MON-YYY')What are the plans now and after the changes?