One more reason for using surrogate keys in a Datawarehouse.

1.  As data is extracted from disparate  sources , where  in each source might have primary keys with  data types or formats inherent to the underlying database, if the same primary keys are are used in the DW , there would be   inconsistencies in representation of data which would make quering  of the database a difficult job ,  so  the surrogate keys are implemented to circumvent these kind of situations .