I would agree that there is very little difference, but the reason why the MCAT alone should be accepted is for comparison. While the DAT is similar it is not the same. So to compare student with a 3.5 GPA and a MCAT score A to a 3.5 and a DAT score of A, it is not fair to either student.
With one test comes an equal comparison from student to student and from school to school. When a school says that the average MCAT is #, you know that includes every student in accepted into the class. Therefore students, organizations (CPME, AACPM), and schools can track these classes and possible see trends which can be used to improve the quality of podiatric students.