In fairness, I don't think lasting injuries like this fit an HP mechanic at all.
In 3e, maybe it'd some house-rule for ability score damage from injury that causes a long recovery and actual mechanical effects. In 4e, maybe it'd be a houseruled disease track mechanism for tracking long-term injuries. Neither one looks like "hit points" to me.
-O
Full HP does not mean "Not bruised, battered, or injured in any way"
It means "I am at my full fighting capacity, perhaps despite some pain."
There's nothing saying a character has zero bruises or scrapes; or that he might not have a sprain. He could have serious injuries but a whole lot of willpower. Full HP just means that any of those negative conditions won't make a difference in the outcome of a fight.
-O
Obyrn, I feel that you're ruling out examples unjustly. Specifically, the Whedonverse examples. At the end of season two, Xander, with his broken arm, had engaged in two fights. In both cases he fought in melee but was hampered, wincing in pain and lacking much in the way of stamina. (He's in the last battle for one round before going off to find Giles, punching someone with his cast and then he's off to rescue Giles.) To me, that suggests low HP a day after his arm was broken. It's clearly not dexterity damage. It's a signifier of lingering HP damage that hasn't healed over night despite healing, hugs and rest in comfy hospital waiting areas.
Giles, groggy and out of it from physical damage, has clearly been hovering at 0 HP for several hours and has to be carried out by Xander. And, Giles, standing with bruises, cuts and broken fingers later on, could clearly engage in a fight if necessary, but also would clearly get knocked out even earlier than usual. He's in single digits of HP after being to the hospital. It's clearly not ability damage. He's in similar shape at the end of the Zeppo, where he used an axe in combat the day before. Both are signifiers of lingering HP damage that haven't healed over night.
Cordelia is out for a week after her fall and impalement by the rebar. It's clearly a slow healing process for HP, not ability damage. (From a fall?!) She's functional a week later, attending school and the Bronze, but significant physical contact (a push) causes her to pop her stitches, indicating that she's still below her top HP. It's a signifier of lingering HP damage. It's a signifier of lingering HP damage that hasn't healed over a week.
Riley in "Who Are You" winces at a sharp tap to the chest by "Buffy". He can't mix it up. But he still has the ability to dust a vampire by exposing it to the sun during a surprise round. It's a signifier of lingering HP damage that hasn't healed over night.
And on and on... I mean, clearly the series does use something approximating healing surges at times (Buffy standing up in the finale of season seven to fight on after a stabbing; Willow casting a spell from her hospital bed in season two). I've pointed out in this thread that I think the series has some examples that fit neither mechanic well (the comas, specifically), but I certainly didn't waste my time posting all of them because I believe that some of them cannot be modeled by 4E's system. I was asked to come up with examples of physical damage that takes a while to heal and impedes the person in physical combat later. I did that, over and over again on period ranging from months to the next day.
