You've all given me more things to thing about if and when my son, a Marine, goes back to Iraq. First of all, they all spend time filling out lots of "in case of death" papers--at least those in my son's company do. They make them out before they go. However, it never crossed my mind to ask him for passwords. Well, one more thing to add to the list.
And if he DECLINES, don't question it.