Most Iraqi casualties have been from car and suicide bombs, and secular violence, the latter of which amounts to gang warfare. Almost all of the incidents coming out of Iraq are in these categories. Most car and suitice bombs have been from foreign fighters. The secular violence is, of course, almost all Iraqis.

U.S. casualties are coming from IEDs, and random gunfire attacks. These are probably the only attacks that can be considered "insurgent activity" against an occupier. These activities are being directly supported and armed by Iran and Syria, mostly the former right now.

How many Iraqis does it take to kill two or three Americans a day on average, using snipers and bombs in roadways? 25 million? 2500?

Most of the population wants the fighting to stop, and the Americans to go home. They also know that if Americans go home too early, the result will be disaster. This is why survey results, even from the same respondents, aren't always consistent between questions.