In game terms, I understand the benefit of perma-marking a foe, so you can attend to other markers, and get the benefits even if that enemy flies away.
(I don't understand how to explain this in the game world - how can a Fighter have any bearing on what the Dragon does to your Wizard buddy if he can't reach the Dragon? - but I have also realized you're not supposed to care for verisimilitude if you want to play 4E)
However, the other benefit discussed, that the mark can't be superseded, I am less sure about?
If the fighter desperatedly wants to be the one who marks the BBEG, can't he just tell his Paladin chum to stay the frak out? (In other words, why use up a valuable power to do something simple communication can do better?)
Slightly confused,
Zapp
First, I don't know if I want to introduce a discussion of verisimilitude in a game with elves wielding two bastard swords, one in each hand, while fighting a dragon.
Having said that, you can
choose to explain this in-game in a way that makes "sense", or you can choose to explain this in a way that doesn't make sense. Same as you can explain a Second Wind as a burst of grit and determination which allows the fighter to get back into the fight, or as "poof! The axe wound disappears!".
I would explain this, in game, as the fighter makes an attack which is so threatening (or even utters a fell oath while attacking that is so threatening) that the target is cowed, unnerved, or forced to consider him a lasting threat. For the remainder of the encounter, the Dragon (or whatever) keeps a wary eye on the fighter, paying attention to him, no matter what else happens. Perhaps the fighter smashes his hammer into the wing of the dragon, almost breaking it, or vows to his dwarven ancestors to kill the beast or die in the endeavor. In any case, the fighter establishes himself as a primary threat, not to be ignored.
Second, this "perma-mark" doesn't, as noted, have to be maintained. It also can't be accidentally removed by someone else who forgets and excitedly announced they are marking the target. Also, as an interesting role-playing opportunity, it allows two characters to have a friendly rivalry. Perhaps both the fighter and the paladin are "glory hounds", and both want to be "the one" to kill the dragon. Perhaps both the paladin and the fighter have sworn an oath to kill the beast, and neither will feel their honor satisfied otherwise. I think that it is an interesting and useful game mechanic which allows certain RP elements which aren't otherwise possible.