I don't personally believe that you should be shooting anything if you don't reasonably believe that you will hit the target. On the whole, a single shot or a "Hey, jerk, I have a gun!" would be enough to stop a robber. People typically do not want to die, and that lizard part of your brain takes over. In this instance, if there was another intruder, I think his buddy would have gotten the hell out of there after hearing his friend screaming in agony after being shot.
Spraying 15 or 30 bullets into a neighborhood is reckless and stupid. People die from ricochets, or get shot by them, frequently enough. The home defender would become a defendant in a murder trial. Last I checked, collateral damage is not an acceptable argument in court.
If you're going to keep a loaded gun with the intention of using it in self defense, you should become proficient in firing it, obviously. But, when confronted with a life or death situation, the adrenaline flows, and your fine motor control is reduced. A larger magazine increases your odds of placing enough shots in vital areas to stop an attacker, or multiple attackers. Nobody is advocating firing away blindly and recklessly. Yes, sometimes the mere sight of a gun is enough to end a confrontation, but you can't count on that, and you need to be prepared to pull the trigger if you must. And you should keep pulling that trigger until you know the threat is eliminated. You don't shoot once and assume the guy's done for the day.