I think that saying is more of a cultural thing and not necessarily relating to the act of being excommunicated by the RCC. I think the the Catholic bishops of NY should tread carefully in dealing with the governor. If they publically dealt with him in harsh mannor then the confusion which could result might cause a backlash against the RCC (After all, whens the last time a public official was publically excommunicated by a bishop?). Look what happened in Russia when St Tikhon anathematized the Communist in 1918? The godless authorities used it as an excuse to attack the ROC even further by claiming that they were disloyal and traitorous. The anathema's were used as an excuse to persecute the Church even more then she was already experiencing. I don't think that such an event would occur in NY State, but still there are a lot of anti Catholic folks as well as lapsed or nominal RC's who could be swayed against the Church if such an event took place.
It probably would be better if the Pope or some high official in the Vatican took the initiative and thus remove the burden of responsibility from the NY bishops shoulders and thus the blame as well.