Come on ppl!!! I'm sure about this..
Non-american singers americanise their accent because in the USA, they'll have fame, they'll be known around the world
Example
The internation singers to be promoted in Latin America are from the USA TOPS... If a singer is only famous in his-her country (non american).. he-she won't be famous here.... MISSY HIGGINS, SANDI THIOM, SARAH BLASKO
Now, non-ame singers are singing with their own accent, little by little... mainly British.. u can see many new british artists singing with their accent, but AUSSIE and KIWI accent are so different from the USA one that they still hide it....
As I said.. Natalie Imbruglia confessed that the musical producers MAKES THEM americanise their songs.. it's sad..
So, how come KYLIE MONIGUE (From melbourne) doesn't sing with the same accent of MISSY HIGGINS (also from melbourne) when you hear Kylie... you ARE SURE she is American...