Also, 7 years of hardcore MMORPG-playing has caused me to see balance as much more important than it really should be. Messageboards such as ENworld too. Actually, we talked about this last week (in my group), and the main concensus was that the internet (and especially boards like these) were probably the best and the worst thing that happened to our D&D.
I certainly agree with the previous poster who suggests that the net in general, and online multiplayer gaming in particular, might have made some of us hyper-sensitive to balance issues which may not, in the grand scheme of things, matter to many players. It most assuredly applies to me.
I do however think that balanced mechanics (classes, powers, talents, whatever they're called) are hallmarks of good overall design sensibilities, and I doubt there are many professional designers out there who would deliberately write imbalance into a game out of some perceived obligation to the source material, or in the expectation that their player base "would probably be okay with it". I just think the world has moved on from there.
This more than anything else is the contribution that video games have brought to the game table.
MMO's due to their nature absolutely have to be balanced. If people think that playing a class in an mmo is not fun, that MMO is going to suffer.
I played City of Heroes for a bit, especially around 'issue 5' when they nerfed some classes and buffed classes for balance. It was needed then. The classes needed to be balanced.
In a wargame the armies need to be balanced, or at least be balanced overall. CHoosing points is another matter.
In an RPG, There are many other factours to consider rather than combat. Though Mage is arguably the most powerful class, I rarely had a mage player that was leader of the party. It was usually the Fighter, or some subclass of fighter (yes even in 3rd edition) that took on the role of party leader (party leader, not leader as defined in 4e and mmo's).
I have never run a game yet where a rogue or warrior felt bored. Balance only became necessary when people got used to "team games" like City of heroes or World of Warcraft. Perhaps you are correct in that "the world has moved on". I would agree but that it is an effect of MMO's. The fact you are practically required to play on a team on an mmo is what turns me off to them incidentally, they should allow for solo play but that is another topic.
Video games that are not MMO's do not necessarily need balance. Oblivion Warriors suffer the same drawback that D&D warriors suffer. In Mass Effect a tech character is far less effective than a soldier. These video games however provide oppurtunity or "Face Balance" as I think cadfan coined. There are plenty of things you cannot do in mass effect if you do not have a techie, and likewise many places you cannot go in oblivion or morrowwind if you do not have a thief.
For me, balance in a game ensures that there are no (or few) truly suboptimal choices. In a balanced game, I will contribute and feel useful playing any reasonable type of adventuring character. I will not be penalized (with a less effective character) based on that decision.
For games that rely heavily on their mechanical aspects (like D&D, vis a vis combat abilities), I find balance is pretty darn important. If my character sucks, I will have less fun than the player whose character is really effective.
Other than the internet, I have never heard of a player not having fun because of class choice. I have heard of it in cases where the DM forced a class upon them. I know in my group nobody ever wanted to play cleric. I made my game extremely faith oriented, so when I DM a game it is less of a problem with them. The fighting classes just about everyone wanted. Perhaps thats anamolous.
I would definitely NOT have fun playing a sucky class. I do not think though, that the balance of D&D as it was really made non casters all that bad.
The only balance I ever strived for in D&D was making sure that my encounters were challenging to the PCs. I managed to make some perfect encounters where about half the party is down and the ones left standing have less than 5% of their hit points left. That is balance as I see it.