Not to mention that a) defibrillation alone without medication and oxygen has a very low success rate and b) not all cardiac dysrhythmias respond to defibrillation. And not all pulseless patients are having a heart attack. Try defibrillating a brain aneurysm or a pulmonary embolism and see what you get. Just like the defibrillators in airports - how many have been used successfully to date? This is good news only for companies that sell defibrillators.
I am an Emergency Room RN, with 8+ years of experience, including Advanced Cardiac Life Support.
Most of the research of which I'm aware shows that early defibrillation is second only to good CPR in the vast majority of cases. Studies from Japan have showed that the most common medication, epinephrine, actually does nothing more than allow a body to get to the hospital with a non-functioning brain, but it has been used for so long by out of hospital providers that it is a very difficult thing to remove from the protocols ("but, we have to do something!") Oxygen is also being stressed less, as research shows that it can cause vasoconstriction of the coronary arteries.
Out of hospital survival rates for cardiac arrest are lower than most people think (as are in-hospital rates, though they are higher. See http://www.heart.org/HEARTORG/... for U.S. statistics). The reason for higher survival rates in the hospital setting are varied, but the biggest reason is that you have trained people nearby, and quick access to the one thing that makes a real difference - early defibrillation of an appropriate arrhythmia.
Early AED delivery in the field could be of great assistance in the right circumstances.
BTW, an AEDs do not recommend defibrillation unless it senses a "Shockable Rhythm," i.e. Ventricular Tachycardia or Fibrillation. OP is correct that there are other rhythms which do not respond to defibrillation, but a) AEDs are good at recognizing them, and b) rates of survival to neurologically-intact discharge are much lower, on the order of a full order of magnitude. A patient with Pulmonary Embolus or Aneurysm (or Seizure for that matter) would not have either of these rhythms.