This is an interesting phenomenon in filmmaking, too. A friend pitched a comedy to the studios a few years ago about a weatherman who gets the power to control the weather. It was really along the lines of BRUCE ALMIGHTY or GROUNDHOG DAY as a kind of "genie out of the bottle" story that they liked, but because it was the same year Katrina hit, they were reluctant to consider it reasoning that people wouldn't want to see a comedy about weather disasters.
Of course, what they don't consider is that the movie wouldn't have hit theaters or television for a year, at least, by which time people would be ready for disaster movies again. I mean, think of all the popcorn action movies since 9/11 that have had skyscrapers collapsing in them.