Chips. Just a matter of taste, really

Chips Just a matter of taste really
How, I wondered, might "natural flavour" differ from "nature identical flavour"? And why, if they contain traces of lime and pepper, do the chips need more flavours plus flavour enhancer 621 (otherwise known as MSG, monosodium glutamate)?

For guidance, I turned to Eric Schlosser's junk food expose Fast Food Nation. In the book, he enters the realm of food product design, where white-coated scientists - the true tastemakers of the global economy - create flavours.