First, it's always a bad idea to reduce military strength for "policital" reasons.
Second, rather than mollify the militants (both internal, and Al Qaeda and others), it would only send them the message that they can get what they want if they cause enough chaos -- so they have every incentive to try *more*, for *more* "reforms" to their liking.
Third, if the militants ever get strong enough to mount direct confrontation, a US military presence would be a big asset to the Sauds.
Fourth, the nations of the Middle East are at a turning point. Do they choose the road which leads to further ties, commerce, prosperity, and peace with the west, or do they make further and further concessions to the forces of Islamic radicalism? This is a big step down the wrong path for the Sauds.
We're still highly dependent on oil from the Muslim world, particularly the Middle East, and will be for the forseeable future - barring some unexpected technological breakthrough. If we don't have a good alternative to the Prince Sultan - and aircraft carriers are not a good alternative - then we must fight for it.
Some will say that we don't have to control the oil. Muslims are just as dependent upon oil revenue as we are upon oil. I don't buy it. The fundamentalists are willing to starve, to die in order to bring us down. Even selling out Israel - our only good bargaining chip - won't help. It would just feed their egos.