Background
The term Russian Oligarch is a common phrase used in American media as well as British Media. In addition, it is a phrase used in Russia as well according to Sergei Guriev and Andrei Rachinsky in the Journal of Economic Perspectives:
In its current meaning in Russia, the term “oligarch” denotes a businessman (and the lists of oligarchs include only men) who controls sufficient resources to influence national politics.
By Russia's definition, an oligarch just denotes a (male) businessman who controls enough resources to influence national politics....which is de facto the same thing that America's wealthy do behind the scenes. Indeed most of the top 10 billionaires are from the United States, and they fill most of the to 50 slots as well. You have to go down to Vladimir Potanin (49 at the time of this question) to find a single billionaire from Russia. The larger collective magnitude of Billionaires in America and outside of Russia led me to ask...
Question
Why are American Billionaires, and other billionaires outside Russia, not referred to as Oligarchs when they have a disproportionate control of their country's politics via their market share as well?