This is nothing new. This never stopped happening. The middle east has been the site of proxy wars for a hundred years, and until the oil dries up it will remain that way.
It's actually beneficial to everyone's economy, because the middle east don't have to worry about spending money developing their own weapons (other than Israel) and then the US/Russia don't have to worry quite so much about the price of oil. The arab nations love their money too much, and would rather buy proven tech from Russia/America than spend a **** ton more developing their own. Then they get their European cars, their Russian caviar, their American business partners, with a lot less questions.
Without these arms deals, America would either have to reduce arms production, therefore cutting jobs, or increase the size of the military and thus increase public spending and more than likely reduces the increasingly liberal public opinion of the administration.