With all due respect to Mustang/Kappa, I think it's completely natural and appropriate to have this sort of reaction to incidents like this. As horrible and ravishing a disease as the AIDS epidemic is, it's become a fact of life in today's world; we all realize, and even to some degree accept, that there will be millions of deaths caused by it every year in developing countries. Even though there are a lot of people fighting very hard to change this, it's part of our daily experience about how the world works.
In contrast, when you have an incident where over 30 college students and professors are gunned down in cold blood in the middle of classes, or when thousands of ordinary businesspeople are killed in one horrific swoop, you can't help but be rather shocked and stunned. Like Mustang alluded to, that sort of thing doesn't (one might even say "isn't supposed to") happen on a daily, or even yearly basis, especially not in a country like the United States. It's so far out of our daily way of thinking, we almost can't even comprehend it. There's also the issue of being able to relate to the victims much more deeply when a tragedy happens closer to home. When I see pictures of people suffering from AIDS in Ethiopia, I may feel for them, but all they're really able to represent to me are faces living half a planet away. In contrast, as a college student, I look at the people who died at VT and see people who could have been sitting next to me in class today...or hell, even my own face. The same is true for a lot of people in the case of 9/11. It may seem like a double-standard to some, and by some definitions it is, but it's also the natural way that we as human beings operate.
