I just finished reading The Emperors of Chocolate by Joel Glenn Brenner. This book documents the history of both the Hershey and Mars empires. Apparently, Hershey "perfected" its blend of chocolate almost a century ago. Their "special flavor" was probably the result of rancid milk enzymes. The company has never changed their recipe since then, fearing to tamper with a sure thing.

When Hershey tried to market its wares in Canada it was a total flop - Canadians like a different form of chocolate. The book talks about what sort of chocolate flavor is favored by different nationalities.

The book also documents Hershey's acquisition of the right to manufacture Kit-Kat bars in the U.S., and yes, Hershey uses their own recipe of chocolate to cover the beloved cookie bar.

European chocolate manufacturers interviewed for the book rate Hershey's chocolate flavor as barn-yard chocolate.