^^ Wouldn't she be the "Showa Songstress" then? Or did an emporer die recently? Even so, Showa would be like Yamaguchi Momoe or Hibari Misora. So yeah, I don't know.
I think the difference is how they influenced the music industry. Utada is just straight up talent; composing and writing most (if not all) of her material. Her MUSIC is what influenced the industry. I think Ayu on the other hand influenced it as a whole, bringing FASHION and a "brown bags to stardom" sort of appeal. Ayu was also the one to introduce the CD+DVD format, I believe. So she really set some standards. As a whole, these two, along with artists like Amuro Namie, Morning Musume, SPEED, and ZONE will be the "Heisei Era".
So actually, with news of Ayu's deafness, this just might be the headline of the Heisei era. I think no other entertainment news (may be besides record concert sales by Amuro) would be able to top this.
@Huaka: I never came across it yet, so I'll look at it soon. The wiki article does have a better explanation of the hearing aids suggested in the article, though. So it's not a complete waste.