From an artistic perspective, in some areas an operatic-style voice is just inappropriate. Operatic vocals on a punk band might be an interesting novelty, for example, but it's not usually what you want; you usually want something more like this: http://www.youtube.com/watch?v=xGjk1Y_j8QE
(From that perspective, metal was a fairly good choice for this interview, because operatic vocals are often appropriate in metal.)
There's clearly a safety margin in what vocal coaches teach, and I think it's safe to say that Ozzy must be over the margin, but the right side of critical.
I haven't heard him in a recent live performance, but reportedly Robert Plant has also ruined his voice. One person said that he "sounds like Winnie-the-Pooh".
The people at the top of any field you will find combine hard work with genetic predisposition. They can be an inspiration sure, but imitating them is unlikely to yield the same results.
Specifically, we're talking not just about "music" here - which has an absurdly broad definition - but "metal," which falls under the category of western vocal-led performance. There are rules to this, and while breaking them might leave you with something that is ostensibly "music," it may well not leave you with "metal," "singing," a "song," or a "performance."
"True ease of writing comes through art, not chance,
As he moves best who learns the steps of dance,
'Tis not enough no harshness cause offence,
The sound must seem an echo of the sense"
Learn the rules, then maybe break them.
Did I just equate my work to Picasso? . . . I think I did!
"Picasso didn't start with painting women with three eyes and square breasts. He knew how to paint a cow."
Creativity always happens when I'm editing what filled the structure. The basic rules I lay down in advance make sure I get to that point.
And to bring this back to visual arts, it's rare to find a good artist who doesn't study references and do thumbnails.
One of my favorite bands is Maiden, mainly for the fact that their songs have the ability to capture the energy of their lyrics. Which is exactly what Ozzy has when singing Iron Man, Crazy Train, Bark at the Moon and even with his modern stuff.
Of modern bands I'm hard pressed to find bands that adequately capture the energy of their lyrics just right. I really only have Coheed and Cambria who can nail so many different musical styles with the right energy for their lyrics.
As for breaking the "rules", the theory goes you have to master the rules to break them. Expressed in a more technical way, once you know the rules, you know when and were it's ok to break them, and you can also adhere to most of the rules while only breaking one or two.
There are always 'rules' to any real discipline. If you aren't skilled in something then of course we say 'he is a natural'. But if you go up to talk to a 'natural' you always find that they worked at it an incredible amount.
Fun read either way though. Her comments on Ozzie were the most surprising to me.