It seems like a simple hunting accident--not really uncommon, unfortunately. Sometimes with a much more tragic outcome.
The only thing that bothers me is how ranch owner Armstrong and White House Spokesman McClellan are making Whittington out to be at fault for walking up near Cheney. I was always taught to be absolutely sure where I was shooting (when hunting) and that there was nobody nearby, certainly not in the line of fire. The guy shooting the gun is the one who most needs to be careful. But that would mean expecting Cheney to admit he did something wrong, even if it was unintentional--something this Administration won't do. An established pattern.
There's no excuse for a shooting hunter, panning in a circle following the flight of a quail, to shoot a bystander. It's clearly the shooters' fault. An accident, but still his fault.
The delay in reporting? The White House was probably hoping the whole thing would never come to light. At least not until they got their stories straight and "interviewed" the local Sheriff to make sure he's saying the right things.