Well, to be fair, the royal family has a somewhat higher risk of targeted attacks against them, be it terrorism, large scale theft (this being the less likely IMO) or assasination, simply due to their status.
Like when the IRA blew up Lord Mountbatten.... whilst the Monarchy aren't an effective target in terms of affecting political change, they're a strong symbolic target.
Another issue is that when someone is killed trying to rob a royal - or even a government - high security building, it will almost certainly be by a formally trained operative (be it army, police or some other). Whereas someone who shoots a burgler, doesn't have the same level of risk assessment training, i.e. it becomes a lot hazier when evaluating their logic. As such, I can understand why a jury may be required to cast judgement on the validity of that action.