I see where you are coming from. I totally acknowledge that Duke is a decent school. It can be compared to some of top Canadian schools like U of Toronto, which also regularly ranks within top 20 in most fields. That being said, I don't really like to distinguish schools by rankings but considering European and Asian schools, both Duke and UofT don't really place within top 20 in the world anymore in a lot of fields. They do in any respectable American sources that ranks based on English publications and citations made in English journals. Then, there are Princeton, Harvard, Yale, Columbia, and several others. There are some traditional American schools that just won't be defeated by anyone's, any rankings, and any places.
Ask any professor in Government field. They will tell you Princeton is a better school. Also, the post was made by someone who is applying to government studies, which is a field quite clearly Princeton does a better job at placing their graduates.