It's weird to say that it "costs" the government $x to have these tax concessions. Money you're not taking is not a cost. You wouldn't say it's "costing" the government to not have everyone paying 80% tax.
Ultimately the government does benefit from these super tax concessions by reducing the number of people it has to support in old age. Forcing them to save for retirement through their working lives. But I agree most of the tax concessions go to those who wouldn't need government handouts anyway.