The fighter does... But as I pointed out, it doesn't matter: on average the fighter who hits harder will have foes less likely to provoke.
This is just not true. The DPR at the margin never really gets to the point where it makes sense, even with very large discrepancies in AC, no other feats to lower that discrepancy[like distracting shield and Daunting Challenge], no secondary defensive powers on the part of the other characters, and very low damage coming from the character.
The only time i could see it really getting there would be with high defense battleraging fighters.
Consider for a second this metaphor. Imagine you walk into a store with 10 dollars and only 10 dollars, no credit cards, no bank cards, etc. You want to buy a CD. All the CD's on the shelves have different prices.
Some CD's cost 11 dollars, some cost 12, some cost 13, and some cost 25.
Are you going to buy any CD's?
A: No. Does the fact that some CD's are less costly than the ones that cost 25 dollars makes you more likely to buy them? No.
Its the same case, the question of "having too high ac so that enemies never hit you over your friends" almost never comes into consideration in practical terms. In practical terms a marked enemy is going to hit your friends when.
A: He is using a burst power
B: The damage you do is immaterial to him surviving an extra attack next round(but will not kill him)
C: You can't hit him for some reason
D: he is not intelligent
E: Some specific thing has happened that makes the value of the attack significantly higher on another target[E.G. he can take someone out of the fight, he can stun a character sustaining a power, etc]
There is only ONE of these where your defense/damage matters... And its only really your damage. And Combat challenge advantages are not high enough or numerous enough[you would need enough bonuses to make people start running out of feats] to make a big difference in this anyway. The monster is going to do this because he will never see a situation where the DPR at the margin makes sense for him to do it.
E.G.
I am playing, currently, a fighter in plate mail with a heavy shield. He is a dwarf, he has 27 AC at level 8[+2 layered platemail]. He has distracting shield, 15 constitution, and 20 wisdom. He had devoted Challenge and dwarven weapon training. He is wielding a +3 Waraxe and does 1d12+16 per hit on a combat challenge[+20 to attack, expertise was free]. At level 10, he will be taking fast running because he is out of heroic tier feats he needs[and +2 speed when charging is kinda nice to let me get more attacks in].
His AC is literally as high as anyones can get at this point and will be getting higher when he moves into pit fighter and picks up plate specialization. There is no chance that anyone is going to think "oh man, its totally a good idea to attack the wizard instead of the fighter" because I am going to ruin their day if they do it. If someone was doing half as much Damage/attack as i was they still probably wouldn't do it, because they would still get their day ruined.[A 20 str fighter would be doing, with a bastard sword and the same other values as me 1d10+11 on a CC with an attack bonus of 18 on his CC, still a respectable 16.5 avg dmg/hit with a high attack bonus]
Nothing you said here invalidates my interpretation. A power is still being used on the foe.
But the power does not include the caveat about triggering an immediate interrupt attack, nor do non-attack based powers that place marks make an attack to set that mark.
You can, RAI, RAW, by all accounts make CC attacks against those. The enemy does not know that they're going to get CC'd until the attack happens.
After that they can infer it.