I think you are viewing this whole potential situation a bit too materially. When discussing strategy we have to remember that perception is just as important as reality. By watching the U.S., Al Qaeda is unlikely to determine that U.S. intervention in Saudi Arabia is assured. The U.S. effort in Iraq is far from universally supported and I believe that the bar for future U.S. interventions has been raised astronomically. Al Qaeda observes the flagging public support for the war in Iraq and probably surmises that America is losing its taste for foreign adventures. Wrong or right, the deterrent value of our foreign policy is lessened.

The proposition of U.S. intervention in Saudi Arabia is further impugned if we accept that Al Qaeda, upon seizing power, would not stop oil shipments. This would be deft move and would rob the U.S. of much of its justification for a war.

The other point, that Samurai has correctly identified, is the idea that Al Qaeda would not be so stupid as to declare Saudi Arabia to be the United Republic of Al Qaeda. More likely, they would operate behind a cover organization. In my article I mentioned Zarqawi speaking through his "chosen political mouthpiece." I was alluding to the idea that Al Qaeda in Saudi Arabia would pitch their coup as a popular revolution against a despotic family. If done effectively, this would also hinder any potential U.S intervention.

But, for the sake of argument, let’s assume that Al Qaeda launched their coup, seized the country, and incurred America’s immediate wrath. There is no doubt that Al Qaeda could not oppose American armored columns. It would be foolish to even try. In that sense, you are correct in saying that Al Qaeda could not ‘hold ground,’ however there are larger issues involved in pacifying a country, as we have seen recently. In Iraq the U.S. benefited from the general approval of at least a portion of the population, i.e. the Shi’a and the Kurds. Even with that body of support the effort has been more protracted and violent than most would have guessed. There would not be any locus of support in Arabia. The violent incursion of Westerners into the holiest land of Islam would elicit a response a hundred times more powerful than that which afflicts Israel. America could tramp around Arabia but hold only the ground on which the tank is parked. Furthermore, I do not believe that America has the will or stomach to occupy Arabia for generations upon generations, and were we to install a democracy that body politic would promptly elect a Salafi radical. We would then be in the unenviable position of trying to depose a democratically elected terrorist.