That's it. It provides moral support and a show of leadership. Especially after Katrina, I imagine presidents will be fairly prompt to appear at the site of any disaster. Bush did not go to New Orleans until the situation had become badly unraveled due to the immense scale of it and poor disaster management on FEMA's part, and he took a sound beating in the media for that one. It could be weeks, if not months, until they get these fires completely out. If Obama waited, he'd no doubt get hammered for looking like he doesn't care.
You are, in a way, comparing apples and oranges. It's not as if a president could visit a hurricane-hit area while the hurricane is occurring. You'd have a hard time even landing Air Force One!
Also, it's not as if action isn't being taken. The president does not need to be sitting in the Oval Office signing checks in order to divert federal funds to Colorado. As I stated above, FEMA and the National Guard are very much involved in the effort.