I don't think that DDN should use a WoW style of aggro (more or less whoever deals the most damage gets attacked) for a number of reasons. The DM is better suited to deciding who his preferred targets are than some algorithm.
That said, I definitely think DDN should have mechanics that allow characters (fighters in particular) to incentivize enemies into attacking them (via a marking mechanic, or something similar). The reason is simple. The brave warrior who protects his charge is a classic trope of fantasy, whether you're talking about Aes Sedai and their Warders (Wheel of Time), Caramon and Raistlin, or the prototypical knight who bravely protects the royal family from harm.
It's something that, as a player, I felt was sorely lacking from D&D prior to the Knight (Player's HB 2, 3.5e). Granted, the Knight had issues on a mechanical level, but it was a step in the right direction. Marking (IMO) was another step in that direction, as it changed the Knight's Challenge (which forced an enemy to attack the Knight) into an incentive mechanic. You didn't have to attack the fighter, but depending on the circumstances it might be your smartest option.
Without a "marking" mechanic, assassins can just stroll past the fighter and assassinate the king he's protecting. The fighter's only chance of stopping them is to kill them before they can walk past him. Such mechanics (or in this case, a lack thereof) promote a rocket tag style of play where MOAR damage is always king, to which I say no thank you.
With a "marking" mechanic, damage is no longer the only thing that matters. It introduces a degree of subtlety to combat. It gives fighters control. Suddenly, the knight with a longsword and shield can have just as much of an influence upon the battlefield as the greataxe wielding barbarian. That's a good thing IMO.
Essentially, while the fighter shouldn't be guaranteed to be able to protect his charges, he should certainly have a fighting chance, assuming that's the style of fighter he wants to be.