SCALLYWAG,
It has been a few years since i touched an A320 but my rusty memory of it is that it is very similar to the boeing and as you stated.
411a,
It is not so much a case of 1 degree of change in oat is insignificant.It is the cooling effect of high speed airflow has on a heated (internally using bleed air)aluminium surface and core temperature changes rapidly with every degree of change of OAT.
However i agree the most important thing is to prevent/rid the surface of ice and therefore ensure safety .
Regards DDG