I think that hit points need to be kept firmly in the realm of "abstraction", or else they really start making no sense, with or without martial healers.
They're an out of character, game mechanical abstraction that measures whether or not a creature can keep fighting, and how close they are to not being able to fight anymore. You almost have to assume that they mostly represent willpower, energy, morale, and grit. Otherwise, it starts being simply absurd that any humanoid person could take such extreme amounts of damage and still be fine.
A dagger does 1d4 damage. If hit points represented solely "real meat" on a person, there's no way that anyone should have more than, say, about 20 hit points. Even that is pretty damn tough. At 20 hit points, you'd have to be stabbed a minimum of five times to drop, and could potentially be stabbed nineteen times and still be standing! (Not only standing, but entirely unhindered by these wounds.) Most people in the world should have five or less hit points. That guy with 20 is a real hero.
How does it make sense that my first-level character (say, 25 hit points) could be laying helpless in a coma, and an average adult male human commoner with a dagger would have to coup de grace him at least seven times to even put him in jeopardy of dying, or ten times to actually kill him? This is a regular guy with a large knife, carefully and precisely stabbing a totally defenseless person in an ideal kill spot (an automatic "critical" hit).
So, say he does that only six times, and then stops. My character gets up, perfectly fine for all intents and purposes, despite having been stabbed in the throat and heart and eye sockets six times while he lay unconscious? And if those hit points represent "real bodily damage", then he's really THAT slashed up, having only 1/25th of his essential biological integrity remaining, but no worries, he's fine?
Oh, and if he waits five minutes, he can spontaneously repair all of that damage to himself, if he wants to.
Seriously, that makes sense?
But if hit points are an abstraction representing "lucky avoidance of serious damage" and "determined will to fight despite injuries" then it can make some sense. Then when you get "healed" you're not necessarily stitching together flesh, you could just be "soldiering up" and steeling yourself to fight on, despite your cuts and bruises. Which makes martial healing perfectly reasonable.
I understand the desire for greater simulationism. Game systems which attempt to realistically model actual physical injuries and their effects on the character are cool, and have many devoted followers. I like them, too. But that's not how D&D is, and it never has been. I submit that if a person is really concerned about hit point loss and restoration being realistic (and representing real physical wounds), that D&D is not the best game for that person.
Martial healing makes perfect sense within the D&D game system, given what D&D takes hit points to be. They are an abstraction, and can represent many different narrative concepts relating to a character's ability to continue functioning. It never has to be, "The warlord yells at you and your broken leg miraculously knits itself back together in an instant." The game system itself never insists that this is so.
Yes, I'd admit that hit points are perhaps even more abstracted now in 4E than they were in prior editions. But really, they were never very realistic or a reasonable simulation of physical damage in the first place.
