Not only because of the war: the rating went down because the government is on a dead-end road - voila! Of money. The rating agency is actually saying that it does not believe that the Israeli government is capable of running the country, the campaign - and only after that, also the Israeli economy towards a better future.
Lowering a credit rating is damage to reputation, but the kind that immediately turns into a financial problem. The government will find it difficult to raise the money for the choppers that it promised to the subjects in Gaza.