The main task of a Guard is the creation of a comfortable playing environment and enforcement of the game’s rules. They receive the armour because of their time they spend helping us and they deserve it.
When a Guard leaves the Clan (without any trouble) he can still use the armour until he takes it off or until its broken. I don't see any reason why we should take that away from him when he spend a lot of time helping the game. If you deserve to become a Guard you can get the same armour but it takes a lot to get into Guards and a lot of time to even get that armour.
Yvil