Media training, whose got it, who doesn't and why aren't the trained doing the talking?

This has been a debate for some time in my circle of friends. We spend years perfecting our ability to talk to the media and then we have to put the top guy on camera. He isn't even believable when he passes you in the hallway and says "how are you doing?", now we are putting him in front of a TV camera? I know there are many PR professionals that don't agree with this, but does this make sense? Engineers design and build very technical things, but, for the most part they aren't good communicators. I have had conversations with engineers and lawyers about the public's understanding of the meaning of a word. This frustration, I am sure has caused many a communicator to role his/her eyes in dismay many times. This came up because I had a student ask me recently, when do you put the CEO instead of the press secretary in front of the camera.