I don't want to speak for any group, but I'm pretty sure that most of us who advocate balance in DDN are using the term in a way that isn't what some others may think. When I talk about a balanced game, I mean the following:
1) No class is strictly better than another. For example, the fighter is strictly better than the warrior in 3E, in a very straightforward way. The fighter has better hit points and feats and the warrior has nothing the fighter doesn't have (which is why warrior is an NPC class). Other classes may be less obviously better/worse in this regard. For example, it's hard to come up with a way the sorceror can be superior to the wizard without getting into edge case stuff like needing to spam a spell the sorceror happens to know but the wizard didn't prepare enough times. Much more often though, the greater variety of spells, the bonus feats, and the faster acquisition of higher spell levels make the wizard strictly better, but there is some room for debate (not that I want that debate here - this is an example not a thesis).
2) No class is able to excel in more phases of the game than others. This is meant broadly. I don't care at all if clerics can't open locks well or bards can't be the best greatsword wielders. If a class has abundant tools for certain broad types of encounters (like "social encounters") while another is likely to be minimally involved or ineffectual barring DM heavy-handedness, that's an imbalance in the game mechanics.
3) No class has all the plot power. Getting tricky now! If one class is built to dramatically change situations through clever choices and another is built to plod along in a useful but monotonous fashion, that's another imbalance. For example, the "healbot" cleric concept is what I would call useful but monotonous. Before cleric spells became so varied in 3E and damage prevention (i.e. killing/neutralizing the other guy first) became so much better than in-combat healing in most cases, some clerics simply cast a healing spell (or condition-removal spell) on whoever needed it every round. This is a vital role, but not an interesting one. Compared to a class that has less obvious decisions, the healbot's job seems unenviable. Sure, he has some resource management to do, but it doesn't take much work to get that right. In other words, "balance" can also mean opportunities to make non-trivial and non-obvious choices that influence the outcome of an encounter about as often as everyone else does.
Balance isn't sameness though. I don't think anyone wants to see essentially the same tools in every class's hands. I don't think anyone is saying that every PC should contribute equally to every actual encounter (as opposed to every broad type of encounter). What am I missing here though - what are elements of balance that I overlooked or mischaracterized?
iserith: The game doesn't profess to be "just like our world." What it is just like is the world of Dungeons & Dragons. Any semblance to reality is purely coincidental.
Areleth: How does this help the problems we have with Fighters? Do you think that every time I thought I was playing D&D what I was actually doing was slamming my head in a car door and that if you just explain how to play without doing that then I'll finally enjoy the game?
TD: That's why they put me on the front of every book. This is the dungeon, and I am the dragon. A word of warning though: I'm totally not a level appropriate encounter.