What do you mean need to sell each week?
A console needs to sell enough to continue to have support from a user, other than, there isn't a set amount it needs to sell. It really doesn't matter if a console is in first, second, or third as long as people buy games for it.
A game doesn't need to sell a set amount each week, it just needs to sell a certain total in order to start making money. For a PC game I believe (it's been a good 1-1 1/2 years since I looked at the numbers) the number is in the area of 600,000 games and around 800,000-1,000,000 for a console game with exceptions on both sides of course. For instance, RE4:Wii doesn't need to sell near the 800-1,000k mark to be successful (make money) while Killzone 2 will have to sell a lot more than the 800-1,000k in order to be successful.
