Standard & Poor’s remained the top rating service in the non-agency MBS market during the first quarter of 2005, putting its stamp on 91.2 percent of the total supply of rated deals, according to a new analysis by Inside MBS & ABS. That was down slightly from the 93.2 percent market share S&P captured for all of last year as its competitors made up a little ground. Moody’s Investor Services rated $208.4 billion of non-agency…