That wire suddenly turns a piece of metal into a shield.
It also diverts the ESD currents away from the sensitive circuits.
In addition, it bleeds the RF energy off the cable shield, so it would not get rectified by the circuit.
Other than these... yes... just a wire.
You asked for some basic reading... you can start with this book, it is in its fourth edition for good reason:
http://www.amazon.com/Grounding-Shielding-Techniques-Ralph-Morrison/dp/0471245186
