Acts of God - Justice & Mercy

I've read many articles and posts, heard many discussions, listened to many commentaries about God's role in Hurricane Katrina. I agree that it was an act of God - He did create the world, weather and all. What bothers me is when people point out particular sins in New Orleans that provoked God to act. The sins of Bourbon Street are committed on Main Street, USA as well. Instead of blaming Louisiana for what befell them, why not thank God for His mercy in what did not befall the rest of us.