Does everyone agree with this? (Does it say explicitly this in the 4E books?)
I wanted to check my books before replying to this. Page 293 of the 4e PH states:
"Hit points (hp) measure your ability to stand up to punishment, turn deadly strikes into glancing blows, and stay on your feet throughout a battle. Hit points represent more than physical endurance. They represent your character's skill, luck, and resolve - all the factors that combine to help you stay alive in a combat situation.
So, a high-level 4e character who is low on hit points because he has turned deadly strikes into glancing blows (and is thus covered in nicks and scratches), out of breath from exhausting his physical endurance, and dangerously close to running out of luck is consistent with the 4e definition of hit points.
It seems like I see a lot of 4E players saying that hp represent anything you like -- possibly disassociated from all physical injury, possibly reduced by Intimidate checks, etc. I suppose that could be a poll question.
It is true that pre-4e, hit point damage was almost always delivered by a mechanism that could conceivably kill a person, whether it was a weapon strike, some sort of dangerous substance or energy, or a psionic attack that overloaded the brain.
However, if you accept the premise that hit points are composed of more than physical endurance and also include intangibles like luck and resolve, effects that curse a character (reducing luck) and demoralize him (reducing resolve) should arguably also be able to lower hit points. Whether this could actually result in death is another matter. If you don't want such intangible damage effects to result in death by themselves, you could add a clause that they cannot reduce the target's hit points to less than 1. Alternatively, you could find some way to narrate how running out of luck or resolve could kill a character. Perhaps a character who is out of luck loses his balance and happens to hit his head on a rock, and a character who is out of resolve is simply frightened to death.