Regardless of the fact that WC match is of a greater importance then CB series, resting a player is still resting a players and its not as if Australia haven't done similar things in World Cup, to make sure they get the right team to play or go through in World Cups before or rested players themselves in World Cup matches. It a joke that people can say its ok if we rested players against Ireland, but if did it against Australia is wrong. Thats just stupid.
Personally im not a fan of resting, as you should always play your best side. But you have to do things to make sure your players are at full fitness for the important matches. Its really the shedule that should be getting the blame, not the captains, players or teams. They are just reacting to unrealistic demands on player requirements.