Both will sell between 7-11 million.
Attach rate is an overrated statistic. High hardware sales come from a high volume of games, and so higher selling consoles have lower attach rates for their best-sellers. Past sales are a far better indicator of future sales than are past attach rates. We have to assume that no regular retail game will have an attach rate above about 40%, but can leave the attach rate analysis at that.
I don't care to make a prediction simply because it feels to me like PS3 still doesn't have an identity, and furthermore I'm not sure which groups buy Gran Turismo. It could sell 6 million or 10 million, and it wouldn't surprise me. Less than 8 million would surprise me for Mario Kart.
"[Our former customers] are unable to find software which they WANT to play."
"The way to solve this problem lies in how to communicate what kind of games [they CAN play]."
Satoru Iwata, Nintendo President. Only slightly paraphrased.
