http://www.wizards.com/DnD/Article.aspx?x=dnd/4ll/20110405 <- Read that Article. Now tell me, what is Mearls forgetting here?
It's certainly true that balance isn't about how much DPR one character deals compared to another, but about how every character feels that they're contributing equally. But I think what Mearls is overlooking is that balance is not just described between different character classes, but also between the party and the Dungeon Master.
If the Wizard blows up armies, the Fighter has duels, and the Bard talks everyone out of forming armies and starting duels in the first place, then those are "Spotlights" for each of them. And the intensity of each spotlight, and frequency of each spotlight, can be measured against one another (Unfortunately, I'd love to use the word frequency to refer to the "color" of the spotlight to better serve the analogy, but it serves better in terms of "how often" here. Sadness).
OF course, it's comparing apples to oranges. A Red Spotlight is not the same thing as a Blue Spotlight, and who knows when the social skills character feels like he's contributed (I'll have an article on that later). But there is one thing that we can look at: the intensity of red, blue, and green taken together, let's just call it white. If each of those lights have an intensity of one, they're balanced against each other. If each of them has an intensity of three, they're balanced against each other. But a white light of intensity one, is not the same thing as a white light of intensity three.
It's very easy to give every player their own "I Win" button, and have them hit it at a relatively fixed frequency. You build a game like that, and every player feels balanced with every other player (at least in theory). But the game isn't just five players-there's also a Dungeon Master involved.
An argument can be made that "If the Dungeon Master wants to win then he should probably be a player, now shouldn't he? The Dungeon Master has to be the one who provides the spotlights, not the one who competes with them." I understand where this argument is coming from, but it's losing sight of the issue. If the balance of the Dungeon Master is rejected entirely, it doesn't matter what the net sum of intensity of balance between the players is. When you account for the balance between players and DM, the overall "difficulty" of the campaign, you have enough information that you can get closer to the "Perfect Game Formula" that we're all striving for.
After all, my redesigns to Solo Monsters aren't intended to rebalance Defenders and Controllers versus strikers-after all, Controllers and Defenders both lost out pretty substantially, and I'd already mentioned that Strikers gain a pretty substantial benefit in fighting solo monsters as is!-but rather in Party/Monster dynamics. It's not enough for the PCs to each be overcoming the same amount of challenges-they have to feel like they're being challenged and, just as important, the Dungeon Master has to feel like he is challenging them.
As a DM with a somewhat "Railsy" style of gameplay, I occasionally hear complaints (from people not in my campaigns) that "If I wanted to follow a linear story, I'd just go play a CRPG." But likewise, if there's no one interested in enjoying the Dungeon Master's side of the story, you really are playing a computer game. And no, Asimov, I Not Robot.