Some people are so incredibly ignorant and naive that it amazes still when I see it, such as the author's premise in starting this thread. What you fail to see, Phokus (and perhaps you should start engaging in the activity suggested by the homonym for your handle), is that al'Qaeda is not aimed solely at the United States. The U.S. is their greatest enemy, yes, but that is simply for the moment because of the power which is present in the United States economically, militarily, and politically. Does that mean with a "victory" over the U.S. that AQ will cease its operations, content in their triumph? Hardly.
The intent of AQ and similar groups, following their brand of Islam known as Wahhabism, is the fundamental destruction of the non-Muslim world, since every non-believer is an enemy of Islam. What does that mean? It means that the US, UK, Spain, France, Japan, and South Africa are all in danger from these people. The US is simply a magnet for the attacks because of its stature, its former presence in the Islamic holy land, its historical animosity with Iran and various terrorist groups, and its support for Israel. The other reasons listed, aside from the US being a secular, non-Muslim state, are used to gain adherents who have different views but the same goal of hurting the West because the enemy of my enemy is my friend. No one ever accused AQ and OBL of being stupid, and since many of those with similar goals (though perhaps not Wahhabists themselves) are radical Muslims, they are among the least "offensive" to the Wahhabists, who might be referred to as "enervators" of religion.
So, is the government of Spain responsible for the attack? No, not any more than the government of the United States is responsible for the attacks of September 11th -- and please let everyone know if you think that's the case because I would love to respond. Did the Spanish government support the US in the GWOT and in OIF (and don't forget the seizure of the North Korean So San)? Yes, the government recognized the inherent danger to its citizens from something as insidious as AQ because it has been on the receiving end of terrorism for quite some time now at the hands of ETA.
The incoming Spanish government wants to pull its troops out of Iraq. In no uncertain terms, that means the terrorists win and only encourages them to attack again, gains adherents who see their success in attacking the "weak" West, and lays out quite clearly the backbone of the Spanish government, which is non-existent. We're all assuming, of course, that AQ is behind this attack. If that is indeed the case, what is the message which the incoming government is sending to ETA? If you attack with enough force, we will surrender. If that isn't the very definition of a dangerous policy, I cannot possibly fathom what is.