没这么少。wharton 有1/3 的毕业生会去读mba。这里：

undergrad.wharton.upenn.edu/graduate-study/

Graduate Options

Many Wharton graduates do not feel the need to pursue an advanced degree, because the knowledge that they gained during undergraduate studies prepared them for the business world so well. In fact, only one-third of our alumni go back for an MBA, even up to 15 years after graduation.