I agree with Dukes. The admissions standards are measurably easier for PT programs than for FT programs at comparable schools. While I agree that there are many smart and capable people at the part time programs, they are not generally of the same caliber of the FT students.
Aside from the numbers, other things point to a difference in student quality. To me, the biggest thing is the number of people in the comparable programs. Some of the top PT programs that come to mind, Kellogg, Chicago, Haas, all have far more people in the PT programs than the FT. Since PT programs tend to draw the bulk of their students from the immediate business area, it stands to reason that their talent pool is much more limited than a well-known program that draws talent from around the world.
Also, many schools do not give their PT students access to their career services. I didn't look closely at PT programs, but I'm pretty sure I recall that either Chicago or Kellogg doesn't (Chicago if forced to guess) allow their PT students access to career services. I believe that recruiters, especially for the traditional high-competition jobs, view FT & PT candidates quite differently.
Certainly, there are many smart and capable PT students, especially at the top schools. However, I believe there is a clear distinction between FT & PT.