Be careful with what you're saying ... by obvious reasons, nukes can't be considered regular units in terms of combat
In fact the AI in civ IV actually had specific code just for nuke usage ( to be precise, it had one for ICBM and other for tac nukes, and the ICBM one is pretty bad ... let's just say that in civ IV AI ICBM never target anything besides cities ). If it hadn't that code , it would not use nukes simply because they are not combat units.