As Olbermann points out, Limbaugh is most likely going on a hyperbolic rant to make it seem like all white people are racists. Looking at Limbaugh's own website it is clear he is speaking from his imagined position of what "Obama's America" is trying to indoctrinate us into believing.
I don't know what is more nauseating, Limbaugh's own racism or the racism he is trying to project out to onto America. I am horrified that he would sit at his micorphone saying there are people who believe school buses should be segregated (with even a subtext of an apartheid level of segregation), that the left sees everything through some racial lens, and on and on. Although he couches this in a type of hyperbolic, somewhat satirical, speaking-plain-the-subtext-of-my-enemy rant it still turns my stomach to hear him say it. I cannot help having a gut reaction to the anger and hatred pouring out from Limbaugh is the inverted projection of his own extremely racist beliefs.