That's what T.E. Lawrence said about Arabs in general, but I believe he was thinking of the bedu, the once nomadic tribal Arabs of the desert. A lot of them live in towns now, visiting the desert when they can to see relatives or to vacation in the "big sandy." An ambassador whom I once worked for used to call that place of blazing and freezing purity the "browner pastures." Some still live out there in the ancestral dirah (the path of transhumant migration alloted to their group by tradition). As this article implies, the ties that bind among those tribesmen who live in towns among the hadar (the civilized as the townsmen think of themselves) and those still "out" typically remain strong, and mobilizable.
There are many Arabs who are tribal in social organization and allegiance but only a small proportion of these are Bedouin (bedu in Arabic). Prominent among tribal Arabs who are not bedu are the Zeidi mountaineers of Yemen. Among those who are bedu, there is a self distinction made between those tribes who are asiil (original and noble) and those who are not. The "are nots" are usually believed to be distantly descended from townsmen or peasants who for some reason moved to the desert. I won't attempt to list the groups. There are a lot of books about this.
The asiil bedu hold a special place in the hearts of those Arabs who believe there to be something special and ennobling about the traditions, literature, and customs of these, the supposed root ancestor stock of all real Arabs. The bedu have highly developed codes of honor, hospitality, and the warrior spirit. The poetry of Antar ibn Shaddad, a half African Bedouin of the Jahiliyah (the time before Islam) is widely admired and thought to be among the best of all Arab literature. In short, the idea of the bedu is the receptacle of a lot of the ideas of modern Arabs as to what they ought to be. This is not true for everyone. Nothing is ever true for everyone. Quite a lot of Arabs think the real bedu, the ones they actually see, are the Middle Eastern equivalent of gypsies.
Are these detractors correct? Yes. Ideals hardly ever really exist in their pure form. The bedu are often lazy, treacherous to those whom they think have no "call" on their honor, venal, and loyal only to those whom they think deserve it. On the other hand, the Jordanian tribes have stood by the Hashemite kings through thick and thin.
I have seen a lot of comments now which question the long term allegiance of the Anbar tribes to the Iraqi government, to the Americans or to anything else, except themselves. This is a valid worry, but one based on a particular point of view. A lot of people, especially in government, are "in love with" the idea of "modernity and the "nation-state." They seek for it with a zeal akin to religion. If creating an Iraqi "nation-state" where there never has been one is one's first priority then tribesmen loyal first to their groups and then to the ever shifting kaleidoscope of their leaders alliances are probably not your "cup of tea." Within that framework of thought the "modernists" should ask themselves if they are like Henry Clay who remarked that "he would rather be right than be president." He was neither.
When I went out to Yemen to work a generation ago, I was told all over Washington that Yemen had become or was becoming "modern' and that tribes as a political and social factor were a thing fast disappearing from importance. When I arrived, I found that this widely held opinion was completely wrong and that very little in Yemen mattered at all except the vitality and strength of tribal life. I have been back several times and this remains true. Ali Abdullah Salih, the president, remains what he always was as a leader of the Sanhan tribe of the Hashid Confederation and a kind of "referee" amongst all the groups. The Westernized sector remains the least important part of the society, no matter what the foreign embassies or "the commander guy" thinks.
This "translates" to Iraq. Tribal life remains vital, especially in the parts of the country with which we Americans are having so much trouble. The takfiri jihadis hate tribal life. It detracts from their vision of a "pure" Islamic life. The tribes need a working partnership with someone who can help them against the fanatics. We need the same thing. This not rocket science, folks.
Will the tribesmen be as loyal as Labradors? No. They are not dogs. We, Americans, of all people should value that. pl