I think there's a distinction between winning six prizes only to have the rug yanked out from under you as opposed to passing up on something and hoping for something better.
Champ should have quit while she was ahead then, especially if she had the car.
I think the Australian way is better: in America you're winning one smallish prize (midway between third IB and the $85 shopping prize) unless you flip over the $3,000 or the Jackpot prizes. Who cares. In Australia you're risking big prizes but there's always going to be something more and awesome put in the kitty, as well as staring down the barrel at a huge cash prize.
Yes, there's risk and yes there will be champions who push a step too far and win just the front game prizes. That is the same as a contestant who is wrong on Millionaire as well. The point of the exercise is the risk, and it makes for really good television. Watching as someone has turned over the biggest prizes on the board and has an eight day march to the $50,000 knowing that the car and $10,000 are safe neuters that excitement. Knowing that a champion just has to win by $1 means those instant bargain/cash decisions are less interesting because you'll never be on $495 coming into that third act needing $35 to win the car, so go ahead, have a punt.