I agree and think its fascinating to see portraits of a person done by a number of great photographers, each showing THEIR perception.
As I've stated before on the issue of portraiture, is the difference in who is paying for the portrait. If the subject pays its a far different animal than if a magazine/publication pays or no one pays.
The whole dynamic of flattery/ego enters the equation when the subject is the one with the money or power behind the creation of it.
As with almost all aspects of human interaction when you "follow the money", you get a far better picture (pardon the pun) of intent and influence behind everything, and a portrait is no different.
The interesting thing is that, at least historically, you could occasionally get away with producing an unflattering portrait on commission - note the JP Morgan "Knife" portrait, which was commissioned by JP Morgan himself of Edward Steichen. There are very few recent examples because "celebrities" nowadays are so controlling of their image that they will often demand to review images during the shoot and will actually delete ones they don't like from the photographers' camera. I'm still amazed that Jill Greenberg was able to take even the base photos she manipulated to make John McCain look like a monster with fangs and blood coming out of his mouth. Even the legit photos she took that ran in Atlantic Monthly, which typify her style of weird plasticized front-lighting with a beauty dish are pretty hideous.