One thing that seems off about many of these predictions is the sales pattern that we've seen over and over again with PS3 titles in Japan. They usually have a huge first week, and then a gigantic dropoff after that, falling out of the charts by week 4 or 5. The Metal Gear Solid games, if anything, should be even more frontloaded than usual. (These are emphatically not casual games.)
I expect that Metal Gear Solid 4 will do 70% of its lifetime sales in the first week. I don't know what that number will be, but lifetime sales in the 500-700k region seem most likely. (You will never, ever see something like 200k first week and 800k lifetime; the sales pattern simply hasn't worked like that.)
End of 2008 totals: Wii 42m, 360 24m, PS3 18.5m (made Jan. 4, 2008)
