Most of us have probably encountered that carcass someone did not recover. Yes, these animals cling to life tenaciously, but we hunters also make poor shots - regardless of the cartridge we choose. In some ways, this moose was probably lucky. It survived the wound. I shot an elk years ago that carried the healed-over remains of an arrow in its neck. How many animals are hit with a more substantial projectile and escape only to die a lingering death shortly afterward though?
I don't follow the logic that taking a bigger rifle to the field cures the potential ills of poor shooting (and we're all capable of that). We should all be aware of our limitations as marksmen. "Yes, that's the biggest rack we've ever seen, but - It's farther away than I'm comfortable shooting"; I'm not comfortable shooting at a moving target"; I'm just not in a good position to take a shot at it." It boils down to discipline.
Yes, someone who just bought a .243 to go moose hunting could probably be thought a fool. However, someone experienced with a .243 will - in all likelihood - be more effective than someone who bought a .300 magnum yesterday. Whatever you choose to shoot, shoot it well.