I'll pray for you

I am quite confused about the concept of praying to a higher power for something or another. Take for example the thousands of people who were 'praying for' Hurricane Katrina victims. While this is a nice gesture, has anyone thought about why this would be neccesary? Does God, widely believed to be both benevolent and omniscient, require people to tell Him in order to know that a disaster has occurred (thus not omniscient)? Or will He simply not help them unless other people ask Him to (thus neither benevolent or merciful)? Or does He simply not desire to help them, in which case praying is a futile act anyway?

Wouldn't a Supreme Being know the thoughts in your head before you even utter them, thus making the voicing of those thoughts rather redundant? If one is going to believe in myths at least make them somewhat logical.