Hahaha come on guys, Amy doesn't deserve such an insult as being compared to Duffy! 
Ok now, I think Duffy has been influenced by Amy for sure!
but she's not the only one!
there's a bunch of copycats now, who are called "the new Amys"
they all seem the same repeated story:
they're from England, under 20 ( Amy's age at the begining of her career ), Jazz and Soul sounds and Tina Turner's stylish black voice.
Few examples of this are this girl, Adele, Gabriella Cilmi ( but that one is not from London I think.. )
Anyway, I shouldn't consider this as anything bad..
On the contrary!
Amy has created her own mark, a new style which is being known after she used it as hers, and if things get better to her ( I really hope so!!!!! ) she'll be one of the greatest talents and voices and will have a place in Music's History.
She'll be a legend, cause she actually is at 24.
Someone as great as her will be an inspiration for many others!
Remember that Amy hasn't invented this style of music.
She took Ray Charles and few others as her inspiration, the same way other new artists are taking her as theirs.
She should be proud of being such an important inspiration for so many people.

Demasiados buitres negros.. tu eres demasiado buena para ellos.