Tit for Tat?

Under the apparent view that we can sue ourselves to prosperity, the Justice Department has filed a lawsuit against S&P.  The civil suit accuses them of being largely responsible for the mortgage meltdown and financial crises.  Hmm…  I guess that’s easier than filing a suit against the Federal Reserve, Congress, Fraudulent loan applicants, Fannie Mae & Freddy Mac, as well as a host of “too big to fail” institutions that received taxpayer bailouts.  But why was S&P singled out over the other members (Moody’s and Fitch) of the ratings agency triumvirate?  The only thing that comes immediately to mind is that S&P was the only one who did this.