I think that intent is a huge portion of that. Stalin bragging about killing more than 20 million of his own people would be "evil".To be fair, the U.S. is not directly responsible for all those deaths - many of them resulted from iraqi on iraqi violence.
But, we were responsible for setting the stage that resulted in all those deaths. I'm sure to an iraqi mother, it doesn't matter whether an errant US bomb killed her children, or whether it was gunfire from sectarian militias.
So, in principle, I agree that Bush has more innocent blood on his hands that Pooty Pute.
There has never been a directed action to kill Iraqi civilians. Nor has the US ever slaughtered defenseless citizens on a wholesale basis.