Near as I can tell, the US wouldn't dare charge Iraq. It's politically and diplomatically unacceptable. That was more than apparent when the US tried to divert Iraqi oil profits to rebuilding the country.

Besides, surely the UN will be taking over most of the required peacekeeping mission soon. I hear that there are already more Iraqis acting as police, militia and other peacekeepers than there are Coalition troops in country. Add UN forces and I doubt there'll be much of a US presence long term.