Answer:
It may be a requirement of the bank. The bank's processes may recognize the deposit slip as such by reading the routing number. The fact that many banks do use a different number for deposit tickets is behind the requirement that many ACH Originators require that a voided check, rather than a deposit ticket, be used to verify the bank routing and account number information for services like direct deposit or direct debit.
First published on BankersOnline.com 8/13/12