http://www.guardian.co.uk/football/2012/nov/02/sir-alex-ferguson-mark-clattenburg-innocent
This seems to be the general argument, but I find it just as unlikely that Chelsea would go through all this chaos knowing the repercussions if nothing racist was said. Seems a lot more likely to me that one man, in a charged environment would snap for a moment and say something, as opposed to all the people this had to clear at Chelsea, to even make the decision to report it, all being sure something happened that didn't.