That has been built up over the notion of "Terror". Bin Laden and company carefully cultivated their image as complete outsiders to western culture, as people who represented some sort of pure alternative to the corrupted west....even though many of the people involved in 9/11 were partially westernized in general, had lived in Europe, and had studied in western universities. The people who committed the Boston bombing, on the other hand, left a large paper trail within the United States itself, that will no doubt be pored over, that will make it very hard to demonize them as the complete Other, as folks who had absolutely nothing in common with other people in the United States. The notion of the terrorist as a guy with a long beard in a flowing garment living in the desert actually benefits radical Islam, in my opinion, because it not only suggests to us that we have nothing in common with them--it says the same thing to them. If you have an oppositional construct like that, reality takes a hike and gets replaced by almost metaphysical constructs and ideas. John Kerry's lamentable declaration that the bombings were the face of Evil, with a capitol "E", is an example of what I'm talking about from the Western side, and is as unhelpful as declaring that westerners are the godless Infidels.