I have to agree with the OP on her opinion of when I person is dead, and the ability (or lack of) other humans to bring people back from the dead.
As a Paramedic I would never consider someone I was working on who had the faintest chance of recovery to be dead until we concluded our resus efforts (regardless of the number of shocks administered).
As Paramedics we can recognise life extinct (as opposed to doctors who can pronounce death, just different legal terminology and slightly more restrictions on us).
So in the following circumstances I can recognise death...
Firstly when it's so unbelievably obvious that someone who has never seen a dead body before would know...
Decapitation, massive cranial and cerebral destruction, hemicorporectomy (think Jaws!!) or similar massive injury, incineration, decomposition/ putrification, hypostasis (when gravity causes the blood to pool and settle in whatever part of the body is lowest), Rigor Mortis.
And then in circumstances where resuscitation would be futile or has been attempted and has proven to be futile...
If it is more than 15 minutes since onset of the cardiac arrest, where no bystander CPR has been attempted, and the person has been asystole (flatline) for more than 30 seconds we would recognise that they were dead (there are a few exceptions to this where we would continue working on them for longer ie hypothermia...they're not dead until they're warm and dead!). Also we can not attempt CPR, and recognise death sooner than this in someone with a terminal illness (but pre hospital without access to medical notes we don't do this one that often) and or if a do not attempt CPR in place.
Submersion (not immersion) for longer than 60minutes
None of the people walking around claiming to have been brought back from death will have met this criteria for death at anytime. They will of course have been very poorly and been saved from dying by high quality modern medical care, but never actually died.