You've got a point about the economy. But even in that regard, in my opinion they are more vulnerable than people give them credit for. Western economies are in full recovery mode, and oil prices remain at ~$40/barrel. Basically, if prices keep the same level as they have recently, SA will have to make some changes, somewhere along the way. Either the military or the social contract, with students going abroad at the cost of thousands of $s a month, just to learn English, will have to suffer. In ether case, SA will be weakened.
But that's mostly conjecture on my part and i don't have the latest data on that subject. So I may very well be wrong.
But just to give you a point of contrast, Iran is right now selling 1M Barrels/day, for which I'm not sure if they're getting fully paid or not. So in my opinion, Iran will be a lot more immune to these price fluctuations than the Saudis.