Here is a straightforward explanation by a mathematician of why doing this kind of tragedy arithmetic is wrong. One key to the argument:

In math, if you're not certain your argument is correct, you should apply it in some novel situations and see if it spits out reasonable results. For example: I live in Madison, Wis., which has a population of 220,000. If I want to compute what the Iraq war would look like in my town, I can just take 0.19 percent of that figure and find that the "equivalent" death toll here is 400 people. As for the Hezbollah attack, 0.00013 percent of 220,000 yields 0.286. So, Hezbollah's rocket attack killed the equivalent of a quarter of a Madisonian—surely an underestimate of the crime's impact. On the other hand, nothing forces us to use the whole population of Israel. The city of Haifa has a population of about 270,000, so 0.003 percent of its population was killed in the attack [Newt] Gingrich cites. The equivalent in Miami (population 362,470) would be 11 people. So, what should we imagine in Miami? Eleven people dead, or Gingrich's 500? The method of proportions gives both answers—not a great advertisement for the technique.

(Also, of course, in this case, many of the victims weren't even Dutch, so calculating the toll as a fraction of the population of the Netherlands would make even less sense. CORRECTION: Power apparently did rely on a calculation that only the Dutch share of the death toll. So that part of the arithmetic works. Although then, since there's only one American death confirmed, from the United States' point of view, this would be only .03 percent as much of a disaster.)