Madoff's marks trusted him because he belonged to their ethnic group. That ethnic group happened to be "Jews" but it would have worked just as well with "Italians", "African-Americans", "Swedes"....
As an Italian American who knows plenty of African Americans, I don't think it would have worked just as well with either group. I suspect it might have worked similarly well with Indians, however.
Not all groups have the same level of in-group trust and out-of-group suspicion.
It has some relation - Jewish communities tend to be quite tight. I work with a Jew runing a consultancy and a large amount of the workload comes from his community connections; there is a level of trust - especially regarding money (I know that is a stereotype but it is true) - established by the common religion.
