Juan Cole disagrees:
Secretary of Defense Robert Gates denied Tuesday that the abrupt resignation of Admiral William Fallon as CENTCOM commander indicates an imminent war against Iran. I think Gates's denial is credible. There is no sign of an American war on Iran, which would involve key positioning of warships, materiel and troops. There is no congressional mandate for such a thing, despite the non-binding Kyl-Lieberman resolution in the senate. A provocation is not out of the question, but it would be a risky move in an election year and could easily backfire on the Republican Party (ask Aznar in Spain).I think there may be some truth to that, at least I hope so. I suspect the thing that may have ended Adm. Fallon's career was the Esquire article. The Bush administration has demonstrated unlimited tolerance of incompetence but zero tolerance for dissent.
My guess is that the real reason for moving Fallon out is not Iran but Iraq, and that he is being made to step down for the same reason that Donald Rumsfeld was. He does not agree with the long-term troop escalation or 'surge' in Iraq. He doesn't believe that counter-insurgency will work in Iraq in the medium term. And as an admiral, he has his eye on potential trouble spots such as Taiwan and North Korea, and is frustrated that the hands of the US are tied as long as it is bogged down in the Iraq quagmire.
Having such a big dissenter as CENTCOM commander is inconvenient for the Republican Party at a time when John McCain is admitting that if he fails to convince the American people that the surge is succeeding, he will lose the presidency. That is, Fallon may have run afoul not of Cheney on Iran but McCain on Iraq. This may be Bush's first favor to the Republican nominee, who after all had a career as a naval officer himself.