Optimizer ignores number of records

[Lite Wait]

The query:
EXPLAIN SELECT
`dw_item`.`dwin_item_description` 'Item',
Sum(`dw_sls_item_dtl`.`dwsi_net_sales`) 'Sales'
FROM
dw_sls_item_dtl
INNER JOIN dw_item ON `dw_sls_item_dtl`.`dwsi_store` = `dw_item`.`dwin_store` AND `dw_sls_item_dtl`.`dwsi_item` = `dw_item`.`dwin_item_number`
INNER JOIN dw_vendor ON `dw_sls_item_dtl`.`dwsi_store` = `dw_vendor`.`dwvm_store` AND `dw_sls_item_dtl`.`dwsi_vendor` = `dw_vendor`.`dwvm_vendor_code`
WHERE
`dw_vendor`.`dwvm_vendor_name` = "IMAX CORPORATION"
GROUP BY
`dw_item`.`dwin_item_description`

(returns)
+----+-------------+-----------------+--------+---------------------------------
-----+---------+---------+------------------------------------------------------
----------------+---------+---------------------------------+
| id | select_type | table | type | possible_keys
| key | key_len | ref
| rows | Extra |
+----+-------------+-----------------+--------+---------------------------------
-----+---------+---------+------------------------------------------------------
----------------+---------+---------------------------------+
| 1 | SIMPLE | dw_sls_item_dtl | ALL | Idw_sls_item_dtl3,Idw_sls_item_dtl10 | NULL | NULL | NULL
| 2871033 | Using temporary; Using filesort |
| 1 | SIMPLE | dw_item | eq_ref | PRIMARY
| PRIMARY | 15 | EAGLEDW.dw_sls_item_dtl.dwsi_item,EAGLEDW.dw_sls_item_dtl.dwsi_store | 2 | |
| 1 | SIMPLE | dw_vendor | eq_ref | PRIMARY
| PRIMARY | 6 | EAGLEDW.dw_sls_item_dtl.dwsi_vendor,EAGLEDW.dw_item.dwin_store | 1 | Using where |
+----+-------------+-----------------+--------+---------------------------------
-----+---------+---------+------------------------------------------------------
----------------+---------+---------------------------------+

there are indexes in the dw_sls_item_dtl table for all keys being used in the inner joins. It seems since the where clause isn't using an indexed field, the optimizer doesn't even consider the number of records likely to be returned by each table. (of course) if I index the vendor_name teh query runs fast, but I can't index every field in that table (since they can select any column) and the optimizer _should_ be considering the number of records in the table (heck even lowly Informix-SE does that). Any ideas? Thanks.