$490 per week sounds like a damn good "concession" to me, especially considering it is not means tested, not asset tested, is granted as some sort of "right" and you only have to turn up to WINZ once a year, if that, for a pleasant little chat - no harassment, degradation or lectures.
My Mother is also on super so I know about all the "concessions" and it's a pretty good racket I reckon.
Furthermore - statistically speaking there is an increasing number of people getting on this racket who have never seen a world war or a real depression but have experienced full employment, free tertiary education and record property gains.
To further compound this - when you do shuffle off this moral coil (likely after being on the oldies benefit for 20+ years) you won't have to pay a dime back due to no death taxes.
So don't complain.
How much are you worth to the bank in profit?
According to your post, you do not have a mortgage, get fee-free banking and it's heavily implied you don't have considerable savings or income. So why should you get a further discount?
Home owners with lending get benefits because the bank makes a profit on their lending.
Business owners (including myself) get some personal benefits because we also have lending, merchant services and business banking with the BNZ.
Banks offer individual and group concessions to get new customers within profitable demographics and to increase profitable sales to existing customers. Profitable demographics are: home owners with lending, businesses, government/state sector and high net worth individuals.
In the case of the Home Advantage credit card, the debt is part of a 'package' and is probably secured against the real estate (I have not checked the T&C's).