According to QI, American chocolate has a particular added hint of a flavour of barf. And As I found in NZ with sausages made with mutton - the market has habituated to a taste and competing products (pork) have to mimic certain aspects to compete. Failure to do so brands the item wrong as well as different, and the result is niche. Since Cabury's became American they started manufacturing in East Europe the taste has changed. For the worse.

A good example is TicTac - masquerading as mints, in reality American with a distinct additional flavour that isn't "mint". Not long ago Polo mints started tasting the same, and soon we saw "original" Polos. UK sales clearly took a hit because the taste was different, ie wrong.

FWIW the best chocolate, according to the GF, is more than 75% cocoa. And never any added flavours. That's her Xmas present sorted!