Actually, average/monthly sales don't mean jack. Installed base does. All a publisher wants to know is: "If I publish my game in this region, will I sell enough to make a profit?", Weekly sales numbers don't help with that.Then what? They will keep selling around 8k units per week just like they are doing now.
You can get to any number by consistently selling small numbers, but what's the point when competition gets there way faster?
Milestones don't mean jack. Average/Monthly sales do.