A "Biblical Generation" is about 40 years, thus most family dictatorships last about 80 years. The reason for this is the founder of the Dynasty is always a master politicians who knows how to organize his country and get the people behind him. An example of this is Stalin in 1920 Russia, another is Augustus in the decades before the Common Era.
Now these Dictators take over and often rule Ruthlessly but have massive popular Support do to the political network they set up (Again Stalin in the late 1920s and Early 1930s Russia and Augustus from the Death of his uncle Caesar in 44 BC till the Defeat of Anthony).
Now when the first dictator dies off he is replaced by less competent people (The Dictator had killed off any competent challengers). You see this in 14 AD when Tiberius Replaced Augustus and in 1954 when Khrushchev succeed Stalin. Now the Second Generation came of age under the original Dictator and have worked together under that dictator, and as such they continue to work together fighting for power within the government but refusing to go the extra step of killing each other. For example when the Ruling elite in the Soviet Union thought Khrushchev was going to fast, he wad replaced by Brezhnev. Khrushchev was NOT killed, just exiled to a Collective Farm (And when Khrushchev had his memoir's published in the West, he stay on the farm was extended, again he was NOT killed). The Second generation had work so long under the original dictator and survived that Dictator that to kill a fellow member of the elite would be a step to far.
Now the problems begin with the Third Generation takes over. Int he Case of Ancient Rome this started under Caligula but he was killed after four years of rule and a member of the middle generation was picked to succeed him (and in turn replaced by a new member of the third Generation, Nero).
The problem with the Third Generation is they have NO personnel memory of the original Dictatorships and have developed connections of their own. unlike the Middle Generation who grew up in fear of being killed by the Dictator, the third Generation had no such common experience to share with each other EXCEPT they belief it is their right to the benefits of Society as being a member of the Ruling Elite. With no common bond holding them together the knives come out and they are willing to kill each other to get their way (For example Nero killing of his Mother and other Roman Elites which lead to his overthrow and the year of three Emperors which put Vespasian in Power and the system started all over again, through more quickly).
In Saudi Arabia the Founder of "Modern" Saudi Arabia died in 1952 (The Same year as Stalin, this is the original King Saud). Unlike Russia, The house of Saud set the Kingdom up as a Blood Family Dictatorship NOT a political family Dictatorship (as had been in the case in Russia and to a lesser degree Ancient Rome). Thus the Middle Generation were not only people who lived under the Original Dictator, but also his blood relatives and siblings to each other. Now Under Islam a man can have more than one wife, but he has to provide a separate house for each, but the houses can be beside each other so all of his children grew up with each other to a limited degree. Some were older and more connected then others but to a degree ALL of them had a human bond to each other more than having survived a brutal Dictator. Thus while the Soviet Union Collapsed in the 1980s when the Third Generation started to fight over how and who should rule Russia (Both Gorbachev and Yeltsin were of this Third Generation of Communist Politic an), The House of Saud has survived almost another 20 years WITHOUT the Third generation taking over (King Abdullah, as was King Fahd a son of the founding Dictator). This Middle Generation will not last that much longer, the youngest child of the founder is at least 54 years old (assuming such a child was born the year the original king died, all the record I have seen point to his youngest being born in 1945 but the records are state Secrets in Arabia to this day, if 1945 is the youngest than ALL of his children are over 60 years of age). Most of the middle generation is in their 70s and 80s.
Like the Russia in the late 1980s and throughout the 1990s Saudi Arabia will be the country to watch for radical change in the coming decade. The third Generation is taking over, slowly but surely, the key is what will that take over entail? Will you have a burst of liberalism like in Russia or a burst of Islamic extremism. In Russia once Communism was viewed as dead, westernization was the only path open to Russia and Russia has a long history (going back to Peter the Great) of Westernization. The opposite can be said of Arabia, they tendency over the last three hundred years have been to embrace Wahhabism form of Islam, the same radical form idealized by bin Laden.
Does this mean Arabia will NOT Modernized? No, such a revolution is possible but with the radical islamic more committed to their idea then are the people supporting westernization I lean to the Islamics to win (Just like the Communists under Lenin won in 1917, it was NOT because he had the Majority of people behind him, but he had the largest group of COMMITTED followers behind him).
On the original King Saud and his family)
http://en.wikipedia.org/wiki/Ibn_Saud