Could it be because Louisiana is a "red" state? Robertson said God punished New York on 9/11. His main political premise is that we should vote Republican to escape "God's Wrath". He couldn't exactly say that Charlie, Ivan, Dennis and Katrina were sent to Florida, Georgia, Mississippi, Alabama and Louisiana to punish the 40% of their combined populations that voted for Kerry.
Besides, the Hedonistic, "sinfull" part of N.O., the French ("Freedom") Quarter was relatively unaffected.