The public's view of things like this seems to be, if the leader isn't actually there at 'ground zero' than they can't fully appreciate the scale and human cost of such disasters. I think there's something to be said for this.
When you watch a disaster (man-made or natural) on television, you're physically and (to a large degree) mentally detached from the horror. There really is nothing quite like viewing something with your own eyes. The best example of this I can give is from my own life. When I was a police officer, the first time I attended a road traffic collision I was confronted with a mangled human body. Nothing in my life had prepared me for this experience. I naively thought that because I'd seen horror films, surgical procedures, graphic news reports, etc. on TV, I'd be absolutely fine when I came face to face with the real deal.
I was wrong. Completely wrong. Nothing can prepare you for the reality of such an event.
I think many people are aware of this fact, either unconsciously or consciously, and therefore place a great deal of importance on the leader of a nation being at a disaster site so that they can both see and smell the reality of the situation.