Basically, as soon as a 'hardcore' game has been out on the market for more than a week, the hardest of the hardcore have already played through it, beaten everything there is to beat, and sold it back to gamestop for $5 towards the next week's game. Gamestop will sell these games to the customers for 50$ (or 40$ on the wii), making a huge profit, and not contributing to the sales totals for the game at all.
As for recent ports, it's you lose out on the committed fanbase, and if a game has been out for 6 months and it's really good like Bioshock, you've probably played it quite a bit, even if you don't own a 360, assuming somebody in your peer-group owns one.
Wii has more 20 million sellers than PS3 has 5 million sellers.
Acolyte of Disruption
