I for one, don´t know how this rank works today. It is possible that the rank has been watered down the last 20 years or so. Maybe even longer. It is also possible that this rank, this position, today, no longer functions as it did 20 or more years ago.
In fact, I can´t remember any of the multiple rats the last 20 years or so describing this position throughly.
So Daps, you might be right.
The Mafia tradition is not what it once was.
In the old times, the consiglieri was always elected by all members of a crime family. He was never appointed by the boss (in contrary to the underboss and the capos) and he should be because he´s main function was to represent the interest of the common soldier in front of the boss.

This is what Bill Bonanno says about the position in his book "The Last Testament" (wich I recommend by the way):

"The interests of the soldate (soldiers or workers, the initial level in the rank of made men) were not generally seen as paramount. Therefore, they needed a buffer, someone knowledgeable in the unwritten rules of our tradition, who could be relied upon for advice and counsel....
The role of consigliere - the second of the two elected positions - was invented to serve as a liaison between the members and the rappresentante (the boss)."

This is how it was supposed to be back then. Apparently it worked and the old tradition was what made the Mafia so strong. Electing a consiglieri was defenetively part of that tradition.