Death and Taxes

According to Alexander the Great and His Time, when a soldier died in battle, his family became exempt from taxes. Now, I'm not sure who all that applied to, or for how long, but why has that tradition not carried on?

Isn't that the ultimate tax that a state can impose on you? I think it's a great idea and one who's time has come again - especially here, where the military's such a small portion of the population anyhow. Wonder how the economics of it would play out?