WHY 72 HOURS?

According to survival experts an emergency/disaster kit should contain life supporting equipment and food that will last for 72 hours.  Hence the name "72 Hour Kit." This is a worthy and manageable amount of stuff every family should strive to obtain for each of its members. My only question is, who are these experts anyway? I want to know who decided 72 hours is the optimum amount of hours to have enough stuff socked away that will help you survive?

  I personally would like to survive longer than 72 hours after a disaster has struck. Three days seems a little pessimistic to me.  I'd like to shoot for 168 hours, or 720-744 hours (depending on which month of the year the disaster strikes), or 8760-8784 hours (depending on whether or not it is a leap year). Of course it might be a bit difficult to cram 168 hours, or 744 hours or even 8760 hours worth of stuff into a backpack or the trunk of a car. Seventy two hours worth of portable survival equipment and food seems like a more workable amount.

Good thinking experts!