Also note that Iran wasn't the only one arming insurgents in Iraq. Al-Qaeda, while fading at the time, were supporting the Sunnis, especially once it was clear the Shi'ites sought rapprochement with Iran and feared its growing influence.
As was mentioned before, the German leadership failed to set up a proper resistance movement, and the German people were plain sick of it all (six years of war and only misery and ruin to show for it). The Allies made sure to prepare for any possible insurgency, though sometimes their overreaction left a bad impression on the Germans. Also, the nation-building of postwar Germany is a prime example on how to do reconstructions and is taught in universities, or damn well should be.
By contrast, the Iraq War occupation was a textbook example of what not to do. The Coalition disbanded the Iraqi Army without trying to keep track of its more dangerous elements, focused on trying to find evidence of WMDs that they completely ignored conventional weapons stocks the Iraqi Army soldiers knew where to find, and the "nation rebuilding" of Iraq post-2003 is a joke. While the Iraqi regime didn't exactly prepare a resistance movement in advance, the Coalition badly mishandled everything, practically allowing insurgencies to develop where none had existed before, and then continued to bungle the issue with their refusal to treat the insurgents as anything but "regime dead-enders".
The French resistance was a cowed but not entirely pacified populace growing discontent under the jackboot of an enemy nation. The Soviet and Eastern European partisans were literally fighting a war against extinction, where failure meant the death of themselves and everyone they ever cared about. While the Germans feared the Soviets would engage in massive genocide in reprisal for the failed attempt to wipe them out, at least Germans had West Germany to escape to (and as it turned out, the Soviets were pretty sick of the killing themselves by then, so weren't out to annihilate the German people).