If Bush says that the earth is round, do you feel you have to assert that it must be flat?
In any case, it is not the Bush White House but its critic, Chalmers Johnson, who did the most to popularize the term blowback.
Where there is action, there is always reaction, sooner or later. If you keep imposing your control and expanding your empire, there are bound to be people who strongly resent your domination, and some of those who resent imperialism do not abide by the laws of war and seek to avoid or minimize civilian casualties collateral to their armed struggle.
Throughout the history of colonialism and imperialism, there have been people who resisted empires, and only some of them have made a distinction between civilians and combatants and tried to spare the former. As a matter of fact, retaliations against colonists, imperialists, and their indigenous collaborators were usually as cruel and barbaric as deeds of imperialists themselves.
Modern national liberation movements, often influenced by Marxism, informed of modern laws of war, and conscious of the need to win the hearts and minds of people at home and abroad, made efforts, some of them more than others, to hold themselves to higher standards of behavior than imperialists, but even they meted out many kinds of cruel and unusual punishments (such as necklacing: <http://en.wikipedia.org/wiki/Necklacing>), albeit primarily against collaborators rather than colonists and imperialists.
After the dual decline of Communism and post-colonial governments born of national liberation movements in many countries, not just mass Islamist parties like Hamas and Hizballah but also Islamist terrorist cells that live and die for jihad and jihad only have grown. The former are liberation movements of the traditional kind, and though their rhetoric is Islam and they are culturally more conservative than communists, their political structure (democratic centralism), ideology (populism and anti-imperialism), and behavior (realism) have a great deal in common with communist parties (most of which were culturally conservative in their own ways and never went beyond populist economics anyhow). The latter, jihadist cells, have nothing to do with such mass Islamist parties and are usually opposed to them (probably because jihadists come from higher classes and strata than most followers of mass Islamist parties who tend to come from the poorer half of society).
What's astonishing, given the record of the United States government and growth of jihadist cells, is not that the attacks on the Pentagon and the World Trade Center happened but that so few terrorist attacks against the empire and its denizens have happened in the USA.
As a tactic for jihadists, the 9/11 terrorist attacks make perfect sense.
The jihadists, all Sunni Muslims from the countries under the undemocratic pro-American regimes, who committed the attacks on the Pentagon and the World Trade Center are ruthless and intelligent. They probably knew exactly how the US government would react (attack one or more predominantly Muslim nations), and how the Americans would react (clamor for retaliation or acquiesce to it), and America indeed obliged them. As a result of the "War on Terror," US hegemony is diminished; the secular nationalist dictatorship of Saddam Hussain, an enemy of jihadists, was destroyed; many regimes allied with Washington, such as those of Egypt and Pakistan, have seen their oppositions grow due to the populaces' growing disapproval of their pro-Washington policy; and many, many more Muslims than before have turned to jihad influenced by their brand of Islamism. What not to like from their point of view? To top it all off, Washington is bent upon its campaign against Iran, a nation whose majority are Shi'i Musilms, whom Sunni jihadists regard as infidels. Osama bin Laden and co. must be very, very happy. Since they are perfect opportunists, they may enlist on Washington's side on the Iran front while fighting America and pro-American regimes on other fronts.
In short, there's no mystery here. -- Yoshie