Let me test this sytem I just jury-rigged. This system is based on a fundemental assumption: Some human life have more value and influence than others. (This could explain why there is much shock if an American dies and less shock when other people from other countries die.) This value can be determined by the wealth of the country within they reside, if a person lives in a country with a high GDP per capita, he has more value than a person living in a country with a low GDP per capita. GDP per capita isn't really reliable at all in determing how much money a person actually has, it is just representive of the nation's wealth. For example, Qatar has a high GDP per capita, but that wealth is concentared in the hands of the (relatively) few and it has an underclass. Still, this system is the best I can come up with, as I don't trust the other systems of nation's wealth, altough I am quite willing to do conversions to, say, HDI, if this system itself is promising.
Let us take the CIA World Factbook's GDP per capita figures of say, the US, and compare that to Somailia. According to the CIA World Factbook, the Somaila's (nominal) GDP per capita is $600, and the US' (nominal) GDP per capita is $47,000. One American Life is equal to that of 78 Somailians. From this you can conclude that 3000 Americans (the casualities of the events of 9/11)=235,000 Somailians.
According to the CIA, Afghanistan's GDP per capita is $800. One American life is equal to 58.75 Afghanis. So, 9/11 took away the equiviliant of 176,250 Afghanis.
Iraq's GDP per capita is $4,000, so 1 American Life=11.75 Iraqis. One 9/11 took away the equiviliant of 35,250 Iraqis.
The country with the highest GDP per capita, according to the CIA, is the monarchy Liechtenstein, with a GDP per capita of $118,000. Rich people live in this country to avoid banking regulations, pay low taxes, and look at the great winter scenery. If one Liechtenstein banker kicks the bucket, it is as if 2.5 Americans died. If one American die, it is as if 0.39 Liechtenstein bankers dies. 9/11 would have killed an equviliant of 1195 Liechtenstein bankers.
This system may be useful in providing exact value of human beings, allowing for one person to really gague how much of an impact a death is. If I said 58 Afghanis were killed by the Taliban, you would shurg. But if I said that the equiviliant of 1 American was killed by the Taliban, it would be such great horror and news to other Americans. Maybe this would be a way to "clarify the picture", if you will.
Maybe.
(EDIT: I know one main criticism. I should not rely on the CIA Factbook and instead rely on figures from the World Bank or the UN. That may be true, but there are times where the World Bank or the UN may not be able to come up with figures, like say, with Afghanistan and Iraq. The CIA Factbook's figures should be taken with a grain of salt, I admit.)