Kind of hard to fight to the death for a regime you know won't be there for long. The Russians fought hard for Stalingrad because they knew they if they surrendered, they and their family members would be killed by the Nazis or Stalin's death squads. The Germans fought hard in Berlin against the Russians so that their families could escape toward the western allied forces. The Iraqis know that we are not going to round up thousands of civilians for the gas chambers or slavery. In fact, the US wants to keep the Iraqi army in good shape after the war, in case Iraq's neighbors get greedy. Lastly, I don't think the Pentagon brass want to satisfy Saddam's wish by fighting for Baghad street to street.