Maybe it's because they've learned from Fox News not to regard Iraqis as human

Or maybe they're just morons:

Americans are keenly aware of how many U.S. forces have lost their lives in Iraq, according to a new AP-Ipsos poll. But they woefully underestimate the number of Iraqi civilians who have been killed.

When the poll was conducted earlier this month, a little more than 3,100 U.S. troops had been killed. The midpoint estimate among those polled was right on target, at about 3,000.

[snip]

The number of Iraqis killed, however, is much harder to pin down, and that uncertainty is perhaps reflected in Americans’ tendency to lowball the Iraqi death toll by tens of thousands.

Iraqi civilian deaths are estimated at more than 54,000 and could be much higher; some unofficial estimates range into the hundreds of thousands. The U.N. Assistance Mission for Iraq reports more than 34,000 deaths in 2006 alone.

Among those polled for the AP survey, however, the median estimate of Iraqi deaths was 9,890. The median is the point at which half the estimates were higher and half lower.