The Clones all sound the same because they all 'Grew' up in the same place. Had the same food, wore the same clothes, etc.
Boba Fett didn't. I take it after Jango died, Boba didn't return to Kamino (someone will have to correct me on this), so for the nest 20 years he was a loner........
So realistically his voice and everything else would be totally different to the Clones.
Yeah??