A retaliation would be taken by the people of Iran as the consequence of over-reaching by their leadership, while a preemptive attack on their nuclear facilities alone would rally them around their leadership.
Since their nuclear sites seem to be so dear to them, there is nothing wrong with destroying them while we are at it, along with their military infrastructure. President Bush should allow our Generals in Iraq to publicly present the proof of Iran's egregious acts, complete with the death toll that could be attributed to Iranian meddling in Iraq.
Though I wouldn't personally care, the world will be much more accepting of a retaliation for acts of war, than they will be of another preemptive action.
Good point.
All the more reason to go after the guys with the messiah complexes.