The issue is less about the price of oil but rather the dependency of each of these countries on that oil revenue. The Saudis and other Middle East countries have avoided the dreaded ISIS-like uprisings largely because they have increased social spending to placate the masses. Without expensive oil there is less money to spend on these social programs and that opens the regimes to increased political upheaval. Similar issue in Russia and Venezuela where oil income is one of the few things keeping the corrupt economy afloat.
Meanwhile, in the US, we are significantly less dependent on oil income as it is a much smaller share of our total GDP. The CEO of Exxon, in a recent article, said they have modeled how to be a profitable company even with $40 oil.
The Saudis are willing to let the price fall because they have enough cash reserves to survive for years at their current level of spending. In Venezuela, they spend it as soon as they receive it.
Saudi social spending is partly importing food staples to the countries of OPEC and neighbors. Saudi has supported Egypt with money for food in the not to distant past. The countries adjacent have vastly outgrown their native agricultural carrying capacity, and are ripe for a famine driven revolution. The behavior of ISIS regarding farmers increases the trend toward sparking a famine crisis.