When a user types 7/8/201x into a DatePicker, 7/8/201 is what ends up getting sent to the server.  I believe an important function of a date-type-specific control or widget is to prevent the entry of bad data.  The picker should not allow the entry of any string that is not a valid date or is outside of the Min-Max range (if specified).  In fact, properly formatted dates typed into the textbox seem to ignore the Min-Max range.

No user entering a date of birth is going to use the month selectors.  He or she will type the date into the textbox.  The datepicker, out of the box, should not allow the entry of invalid or out of range dates. The developer should not need to write a custom validator for behavior that virtually everyone would want.