What those who put out salary data for college graduates don't tell you

Are the higher salaries for people from the Naval and Military Academies due to the quality of the schools or the quality of the students?  For example, might it be that the students who go to those schools are driven to work harder or is it because they are smarter?  Indeed, that point applies to salaries for all these top schools.  Often it is only those students who are driven who can make it into these top schools, but that extra drive might help them earn more anyway.  Unfortunately, the type of numbers shown below don't deal with those issues.  From the Wall Street Journal:

Top Schools, Median Starting Salary 

1. U.S. Naval Academy at Annapolis ($77,100) 

2. U.S. Military Academy at West Point ($74,000) 

3. Harvey Mudd College ($73,300) 

4. Massachusetts Institute of Technology ($68,600) 

5. California Institute of Technology ($68,400) 

6. Colorado School of Mines ($66,700) 

7. Rose-Hulman Institute of Technology ($65,100) 

8. Stevens Institute of Technology ($64,900) * 

8. U.S. Air Force Academy ($64,900) * 

10. Thomas Jefferson University ($64,400) 

Top Schools, Median Mid-Career Salary 

1. Harvey Mudd College($143,000) 

2. U.S. Naval Academy at Annapolis ($131,000) 

3. California Institute of Technology ($124,000) ** 

3. Stevens Institute of Technology ($124,000) ** 

5. Babson College ($123,000) 

6. Princeton University ($121,000) 

7. U.S. Military Academy at West Point (120,000) 

8. Brown University ($119,000) + 

8. Harvard University ($119,000) + 

8. Stanford University ($119,000) +