Well first of all I don't think that's the reason the majority of people complain. People complain because they want what other people have/are getting (in this case loot from mobs from DEs). Also I don't think they will increase Mesmer AoE to address this as that would have implications toward other aspects of the game (PvP balance for instance).
Remember that they are have a DE scaling system in place, and I believe for some of these smaller DEs they limit the scaling factor to some level, but for the larger DEs they either don't have a limit or have a much higher limit (e.g. the DEs associated with defending the Temples in Orr). The problem here would be the QA of the scaling effect at these lower DEs.
Secondly it is also bad design of the DEs themselves. There was one in Orr you defend a town where mobs spawn and are actually invulnerable while they all run into one spot, where they then become vulnerable to damage. It's no wonder people farm these DEs. This is simply bad game design.
The precise mechanism of the DE scaling system is where the complication arises: from what I can tell, they scale up the difficulty by calculating how many different people are hitting the event mobs/boss, basically how many people are involved in combat. Say a mob starts out with 100 hp, two people start hitting it, each takes away 10 hp, the mob would be left at 80%. Then the system calculates the situation and scales up the health pool to 180 total, but it doesn't make sense that the mob's health go back up right? So instead we take that 80%, multiply by 180, the mob now sits at 144 hp, but to our naked eyes we won't be seeing a difference in its hp bar as the green bar doesn't suddenly jump up. It's all very nice and cool.
Now, what happens if that first hit is by, say, 20 people at the same time? The mob simply dies. Or if it survives, it's going to have 5% health left, and no amount of scaling is going to save it from certain death. It also doesn't make sense if all of a sudden the mob's health stops dropping because it's been suddenly scaled up 20 times, so I'm sure they take the derivative somewhere in there too, which ultimately results in trash dying very fast when there are lots of people, regardless of scaling.
Bosses and veterans/champions don't have a problem because they start out really high already, unless you have 100 people hitting it at the same time it will most definitely have time to adjust to the proper level. Trash mobs however, you can't make them strong to begin with or else if 2-3 people are on this event they'd be completely overwhelmed.
So in this situation, you have a few options: faster polling (not even sure if this solves anything major) which sure as hell will burn of lot of CPU from ANet, changing damage calculation structure which then trivializes the whole projectile/combo system, or have DE mobs' health bar jump up and down and up and down as more people join the event, eventually leading to player hostility against each other and many many confused people... As you can see, it's not a straight forward answer.
Personally, if I ever really need to farm for things, I'll probably just grab my Guardian and farm DE on her... It's not like we can only have one character.
Edited by CepaCepa, 19 September 2012 - 10:35 PM.