Umm, let's give this a try:
x = how easy it should be a team to make the final four (calculated by 17 minus seeding, so a 1 seed would have x = 16 and a 16 seed would have a 1)
y = percentage a team is Duke
z = ease of making the final four
z = x+2y
So Duke's x = 16, and y = 1.
z = 16 + 2x1
z = 18
This is 2 higher than any other 1 seed, as all other schools are 0 Duke. Does this explain it?