You nailed it for sure on the Warmth. No one sounds the same.
Its just like putting on your old comfortable sweater.
(At least when you listen to the songs such as ACC.)
Then the presence of a really good friend for the more poppy stuff such as Gourmandises n L'Alize.
Though when I first saw this thread and before I read your post. I was thinking
her voice is good but can't be compared to someone with style within their voice such as the likes of someone like "Jewel" , listen to Who Will Save your Soul and she wins hands down.
I totally understand what you're getting at though and She is for sure among my favorite voices.