I live in Wayne, NJ. When the spring rains hit north NJ, Wayne is always on the news: there's a corner of the town that floods every year.
I live on a hill - like Dave E's case - if my house floods, where talking floods like Noah's time.

Fortunately, I don't live next to a stream, so I am officially NOT on a flood plain.
However, I am certain that those folks who live in my town that are in the flood plain are required by law to purchase flood insurance. Maybe it's different in Mississippi and Louisiana - I dunno. But like it was said above - if you live at or near the sea and your house is at or below sea level, it should be a no brainer that you need flood insurance, especially if your area is known for its hurricanes.
My $0.42,
-Z.
PS: I guess it's Bush's fault these people didn't have any flood insurance...