Here is the way my logic works:
They found a single, albeit highly notable man, in war torn Iraq who was attempting to hide from them. People are hard to find, you cannot use metal detectors, they move easily, and can slip away after a tip (he got away from the initial bombing raid). We cannot find Weapons of Mass Destruction (WMDs). WMDs are a lot larger they are a lot harder to move and they show up more easily on things like advanced radar systems.
To me finding Saddam Hussein proves once and for all, there were no WMDs.