Excel 2013 & Oracle query - Date in where clause

Hi  Experts,

 I have a powerpivot report which pulls data from oracle tables(Siebel).

The first query is

Select ROW_ID, CREATED, NAME from S_ORG_EXT where CREATED >= '01-JAN-2013'

The query hits oracle exactly as shown above. But for some reason oracle ignores the where clause and pulls all rows.

Later on we changed the query to

Select ROW_ID, CREATED, NAME from S_ORG_EXT where CREATED >= to_date( '01-JAN-2013' , 'DD-MON-YYYY') and it works fine.

Does anyone know why this happens?

Thanks,

Aji Paul.