Party Balance: The One Balance I Don't Care About

  Players: "We wanna play four Halfling Rogues."
  Some DMs: "Oh, no, no, there should be only one Rogue, the others should be a Magic-User, a Fighter and a Cleric."

  Players: "We wanna play four Halfling Rogues."
  Me as a DM: "O.k, as long as no one minds that other players have the same overall abilities."
  Players: "Nah, we're good."
  Me as a DM: "O.k, let's begin."

   I started thinking about this a while back when in a message board someone was discussing module compatibility with Lamentations of the Flame Princess and pointed out how because in that game Turn Undead was a spell instead of a class ability with unlimited use, any modules with too many undead should have some undead removed from it. (It also has to do with the very next post that I'll be writing after this one, but I digress.)
  In other words, many go into D&D and other similar games thinking that this balance of chosen classes should be automatic in a gaming group.
  It certainly doesn't bother me if players do decide to go for that balance of classes between themselves but I have never felt the need to explain it to new players, always preferring that they choose the class that they want to play the most. The one they'll have the most fun with.
 
  This also brings me to the following: What if you have an adventure that NEEDS a Cleric, and the Cleric dies on that acid trap in Room #3? What then?
  Honestly I see adventures that require one specific class to work as being the same as an adventure that will stop dead in its tracks should the players miss one single die roll, like a Ranger's Tracking for example.

  Some DMs: Oh man, you weren't supposed to miss that die roll. *Proceeds to give the information to the players some other way so that the die roll actually never mattered in the first place.*

  In other words, if I am browsing for an adventure I will certainly not get one that says "Requires a party with a Cleric."
  O.k, maybe one exception where I have been interested in such products before is the series of 1 on 1 adventures from Expeditious Retreat Press, for obvious reasons.