It seems we have the idea of "game balance" on our minds recently (see also Dreams in the Lich House and Gothridge Manor). It's nice when great minds think alike ;)
Beedo over at DinLH takes a wider view of things - is the world balanced unto itself? Why aren't ogres and dragons running roughshod over everything? I think this is a question DMs need to aks themselves, but more so when it comes to the campaign itself.
In other words, while each encounter does not, and more likely should not be "balanced", overall the campaign itself probably should be relatively balanced. Maybe balanced is too strong a word in this case. The players' goals should be attainable with good playing and a bit of luck.
The reason campaigns setting such as Midnight (which i think is an awesome but flawed setting) have trouble finding an audience is that the players are pretty much set up to fail from the start. Failure is fine. Failure gives value to success. When failure is pretty much preordained for the end of the campaign, there isn't much value even to small successes along the way.
I am not saying that the PCs' success should in any way be preordained. Doing so removes true choice and the ability to truly success from the players hands. No, what I mean is that there should be a legitimate way for the players to "succeed" in a campaign's over arcing goal. Actually, there should be multiple ways - not all of which can be thought up by the DM in advance, as players, good players, think out of the box.
If we as DMs challenge the players, we will be rewarded by stronger game play from our players and more fun for everyone in the game.
Remember, success only has value when it is truly earned.