Um...maybe because everyone in the path of a Cat-5 storm doesn't live in a place that, as lil_l_moses points out, is "below the level of three adjacent bodies of water." It doesn't take elabourate flood-control structures and millions a year in energy costs to keep Miami Beach from filling with water at each downpour, does it?

There are a lot of factors--from basic geology on up--that differentiate NOLA from other places, not just the skin colour of the inhabitants. You wouldn't know it from the way most people are talking about the situation, though.