But they are a real-time condition tracker. It's just that the quantity they track can increase as well as decrease. The only difference is that HP are no longer as strictly ablative. This is no different from a tiring runner getting a spurt of energy/speed at different points during a race. This happens even though, on the whole, the runner's energy level is decreasing.
OK
For RC (please tell me if i am correct) i believe he wants HP to at some level model "real" injuries. While there are issues with previous editions (high level fighter HP vs low level fighter HP) he can more easily use the HP system to generalize true wounds.
In pre-4E paradigm even if some of the HP damage a fighter takes is luck, skill etc. at some base level some of it is real injuries which is why it takes days to weeks to heal.
In the 4E paradigm none of the damage is necessarily real. Now you can narrate it however you wish (and this can be a strength) but it does not really map to "injuries" in a quasi-mechanical sense.