Not sure if this has been addressed but your example of Halo 2's minimal boost of sales is a bit flawed. Halo 2 was released near the end of the Xbox's life and was not the first of the series to be released on the console. Many people wanting to play Halo 2 already had their Xbox because of the original Halo. There may be a significant number of people who have waited to purchase a 360 until Halo 3's release. Those who waited made the smart move because now they can purchase the revised hardware at the discounted price.
Whether it will happen, I'm not sure. I think the Wii may also rise in average sales with MP3's release if Nintendo has more out there so the distance may be even larger than you give.
To cash in my CC rewards points for $300 in Circuit City gift cards to purchase a 360 or not: That is the question.
