Standard & Poor’s remained the top rating service in the non-agency MBS market last year, although it saw a little stiffer competition from Moody’s Investor Services and the entry of a new player in the market. S&P rated $805.0 billion of non-agency MBS issued last year, equaling 93.2 percent of the rated portion of the industry. That was down slightly from the 93.5 percent market share the company claimed back in 2003 but consistent with…