Cornices certainly do have a protective function.  No doubt in my mind whatsoever.  If cornices have been removed from a building, expect more rapid deterioration of the facade below the cornice.

Of course, the efficiency of the cornice will influence the extent of the protection ... if the cornice is not water-shedding, with a good drip, then it will not work well.

If you need me to find you some Australian examples, I will see what I can do ...

Regards

david west