Here in Australia we have a wide range of things we can redeem points for - flights, accommodation, car hire, "experiences", travel goods - I can even get supermarket gift cards.
A lot of Australians go to Japan to ride the high speed rail. It seems logical to me that you should have an option to redeem your points for a Japan Rail Pass. Some people have plenty of points but are cash poor so having that option, even at a bad exchange rate, is still handy.
Of course one could always buy 6 weeks worth of supermarket vouchers (6 x $100) and use the money saved to buy the rail pass that way. However it would be great if Qantas or Virgin offered a good value alternative way of redeeming points for rail passes (including Eurail).