This cannot be an explanation because the top Objectivists were not Ayn Rand's friends before she founded Objectivism.
Interesting. Can you give an example of another such ideology?
Yes there is a hierarchy because some of the Objectivists have spent a lot more time and effort studying Objectivism than others and are simply more prominent in the public eye. Lets take Leonard Peikoff as an example. He is a professional philosopher, a professional Objectivist, as well as having the title of Ayn Rand's heir. This definitely qualifies him as being the "top" Objectivist.
BB and NB were heavily involved in the Objectivist movement at one point in their lives therefore I feel this qualifies them as being included in the sample.
The Spiechers are ethnically Jewish as well if I am not mistaken as is David Veksler the owner of this forum (again I'm not sure correct me if I'm wrong).
That Jews don't make up that much of the population, yet dominate the top ranks of Objectivism needs an explanation. I am leading towards the explanation that Jews like to make money and that Objectivism promotes this as top virtue, therefore the most enthusiastic Objectivists tend to be Jewish and rise up the ranks.