Your being too literal. The developers came implement anything they want so long as it works with the story line of destiny and it would be easy to add something like the vanguard decided that their only true weakness is losing their ghost so they make them more durable and able to withstand attacks by armoring them and giving them weapons to perhaps fend off attackers to give them enough time to revive you. They are able to take all the attacks they want when they are in the middle of a hack and your supposed to keep them safe. But no matter what happens they won't get destroyed. The developers can implement anything they can think up.