Looking at Tuesday's results, it's even it's even harder to argue that demographics aren't the primary driver in voting in the Democratic contest.  As Adam Nagourney writes in the NYT:

The Obama Democratic Party is made up of younger voters (under 44), blacks, white men (to a more limited extent) and independents whose show of support accounted for his victories in states like Missouri. Their level of enthusiasm for Mr. Obama — their excitement about the possibility of an Obama White House — is palpable in their response to him, or in any conversation.

The Clinton Democratic Party is the party of women, older voters, Hispanics and also some white men. A Clinton rally may not have the energy of a rock concert the way an Obama rally does. Yet the older women who have embraced Mrs. Clinton as the culmination of years of hope and other core supporters are no less passionate in their intensity and devotion.

It's more accurate however to say that white men are the swing group. White men in California, Missouri and Illinois went for Obama, but in the South, Massachusetts, and New York they went for Hillary. 
Even more, accurately, young men went for Obama pretty much everywhere, older men went for Hillary almost everywhere.  Without a dog in the fight, middle aged white men appear to be the swing group that will determine whether a woman or black man is the first to capture their party's Presidential nomination.

Who says were in the post-ironic age?