I just recently started posting on this site and came across this thread and I find it interesting. There were some interesting points made but I think the problem is just that the PBH and other books don't have the space to make too much reality out of fantasy.
I created an NPC 3.5 ed that was 100th level (wiz/sor/spellfire/archmage) just as an excercise (I was remembering the old Bloodstone Pass adventure book that had a 100th level paladin as a prerolled PC). I gave him a history and reasons for his level and age was one (human but 2200 years old). In thinking about this I thought of the superelf problem and here are my ideas.
It says in the books that the elves are contemplative and take a long time to do anything. So for politics I would think that they spend a great deal of time and thought on what this decision will affect two centuries from now etc and then two centuries later the problem has changed around them making the decision moot. But in PC classes and such think of it like this: a human wizard learns his two spells he can cast at first level and then levels up to get more power as soon as possible, an elf however wants to learn every spell and more importantly why the magic works. "Why does a fireball use bat guano and sulfur instead of tar as components?" etc. Basically due to the human's short life span he is a meta gamer, he doesn't care why he can blow things up he just wants to know how. Inevitably the elf realizes how much his power affects the world (think Dark Sun setting) and doesn't throw around the big guns. Also the elves craft High Magic which generally has a very costly component (usually the lives of several powerful elves) and keeps their numbers down.
Someone above mentioned money and the wealth that comes with time. My response to this is: a minimum wage job over 2000 years still lands me in a pathetic little apartment up to my eyeballs in debt. And even in long lived societies someone has to muck out the horses stalls. In all the books I have read with elves in them it states that they "grow" their homes out of the trees or out of crystal and stone. How much does it cost to grow a mansion? High level wizards charge a premium price just to cast detect magic what will they charge to grow a mansion out of trees? Their economy would take into account time. What are the taxes on a 10,000 year old estate? What's the interest on a 300 year mortgage? With so many years of economic decisions to make they are more likely to hit a disaster (natural or poor choice) that bankrupts them; wastrels in the family; war etc. You would see a tiered society just as we have. (rich elves still want to keep the status quo)
Despite their long lives in general elves only have one or two children. And their biggest enemies, orcs, seem to sprout fully adult from the trees every season. The idea of 'culling' has not worked with orcs so why would it work with any other race. And all of the great epics show that enough throw away orcs can over come any fortification or master swordsman etc.
Last the elves are for the most part a race that leans towards good so they don't tend to enslave and conquer. This also makes them great heroic martyrs. They tend to throw themselves on the blades of their foes just to save the girl. Or they die to the last trying to hold an already fallen city.
In the thread everyone seems to be dealing in absolutes: All elves live to be 1200 years old so why aren't they all epic level whatevers? I'm not picking on your theories Kyr (they just summed up everyone else's and had serious thought in your rebuttals) but your personal discipline has led you to a remarkable juggling of "classes" in your real life. But how many people have you seen in your martial arts training quit? How many failed teachers were there from your graduating class at school? How many people failed in bussiness that you know? Then ask yourself how many people can list all three of those as successful "classes" in their life. We think of D&D PCs and NPCs by what/who we interact with in the game but how many NPCs are there in the town that have no useful information?, no description? How many people do we not see in the towns that our characters pass through?
This goes back to what you said earlier about real life with science making longer living people: the superelf isn't the problem; think of the damage a short thinking 1000 year old human can do. He strives and strives as if he will live a short time but instead will live forever, a race like this would be made up of all epic characters. How fast would we screw up our world then?