I was curious too why DOB's were being required for W-2's.  As a test, I entered dummy DOB's for a few employees and submitted them.  The current status says the agency accepted them and they were successfully processed by the tax agency so unless I get a future notice, I do not believe that DOB's are required to file W-2's.  Looks like QB is requiring them only for benefit purposes (and not exactly sure why they need DOB for benefits since as far as I know QB doesn't offer benefits!)