From the perspective of All Souls, they do want exams that only a few can pass. The goal of this kind of exam is to identify original and insightful thinkers.

I presume that it is hoped that those who enter All Souls will make original and long-lasting contributions to their field of endeavor.

In the natural sciences, a similar effort is supported by the Howard Hughes Foundation at Janelia Farms, as described here: http://www.nature.com/news/research-at-janelia-life-on-the-f...