Interesting read, thanks for sharing!
As hagan_massey said, ayu's attraction lies in her live performances. Not that her studio versions are worse or anything, but the power of her live voice is what makes me love her singing. In my playlist, the mp3 rips of her concerts always get more play than the studio version, and when I feel like listening to a particular song, the first version I look for is the live version.
I agree with the article about the portato, ayu's really good at that, and I'll always love how she does it in Fly high.
Singing with only her throat voice is indeed damaging, though, I wish she'd use her head voice more.
The only song I can recall ever hearing her use her head voice is the last part of ad-lib in GREEN. But that's what I respect about her. It's hard not to use head voice when singing at all, and ayu seems to be able to do it quite well. ^^