How about this explanation of hit points:
Your character has a certain amount of "life energy" inside of him. Hit points are simply a unit of measurement of life energy, in the same way that liters are a unit of measurement of volume. When you are hit, the "life energy" is spent to stabilize the wounds and allow you to keep fighting. When you have no more "life energy" this process no longer works and you fall unconscious.
This explains pretty much all the features of hit points.
Why can you survive being impaled by a spear? Because the magical "life energy" stabilizes the wound.
Why do you fight just as well reduced to 25% hit points as you do at full hit points? For the same reason your cell phone gets just as good reception when its battery is only 25% charged as when it's fully charged.
How do healing surges work? They're just another form of energy that can be converted into "life energy", in the same way that a battery converts chemical energy into electrical energy. This also explains why some magical items require healing surges to use.
Why do you keep getting more and more hit points, and increase your healing surge value, as you go up in level? Because your internal "life energy" system gets more efficient.
Why can you recover all your hit points and healing surges in just eight hours? It's just like recharging a cell phone, except that instead of plugging into an external source of power, there's energy just floating around that you can extract.