"So what *can* we learn from catastrophes like Hurricane Katrina and the Haitian earthquake?
I think the most important lesson may be this: there are things which we are powerless to prevent or even to predict. It's tempting to blame natural disasters on some shadowy conspiracy using secret weapons. That implies human agency and human control. The Elders of Zion, Bilderbergers or Illuminati are less frightening, on an existential level, than the idea of random chaos rearing its ugly head when we least expect it. The secret societies are run by humans (or, if you believe David Icke, by sentient reptilian aliens). You can reason with humans (or even sentient reptilians): you can plead your case with them and make them understand. There is no negotiating with a hurricane or an earthquake; there is no appealing to the emotions of a mudslide or an outbreak of disease; there is no bribing a volcano or a tsunami.
Vodou is about gaining power, but it is also about recognizing the limits of one's power. Vodou recognizes that there are mighty forces in this world which are not human and which have never been human. Some of these forces you can bargain with: others can only be avoided to the best of one's ability. Vodou does not promise its devotees that their lives will be free from suffering or want: it is about doing the best you can with what you have.
Another possible lesson may be this: the universe does not revolve around us. Most of the proposed "answers" to the question of disaster come from a very humanocentric worldview. But what if humans are just one part of Gaia, and not even a particularly important one? The world got along just fine for eons without human beings: it might get along just fine for several more eons without us. Instead of earthquakes being a response to man's sin, why not consider them a release of pressure built up within the planet - pressure which must be released lest it threaten the entire system? The planet does this not to punish us or to educate us, but to protect itself. Our suffering is just collateral damage, something which has little or no impact on Gaia's continued well-being.
From there we might come to a third important point: the universe does not exist to teach us or to protect us. Responsibility for our education and well-being as humans rests squarely with us and with our fellow human beings. As Frank Miller said in The Dark Knight Returns, "the world only makes sense when you force it to." If you want to find a spiritual lesson from disaster, it comes in our response. In helping our fellow man in need, we fulfill the purpose of our incarnation: in bettering their lot, we better our own. Rather than contemplating why these things happen, we do better to ask how we can ameliorate the suffering they leave in their wake."
ETA: I would add that one "why" we can address is "why are the effects of a disaster worse than they have to be?" No one could have averted Hurricane Katrina, but its effects were made dramatically worse by decades of bad decisions that made the poorer parts of NOLA uniquely vulnerable. Similarly, would the devastation in Port-au-Prince have been so comprehensive if Haiti wasn't the poorest nation in the hemisphere, with terribly fragile buildings and a completely bollixed infrastructure? We may not be able to prevent or even predict a disaster, but we can predict what happens when it strikes. As well as helping after the fact, we need to work to make sure that when the inevitable happens, we have done all we can to minimize the effects.