Joemanji on 03 September 2007
This source isn't reliable. My guess is he misinterpreted the press release from Amazon.com In fact he even quote them!
Amazon didn't provide numbers as well, they just stated that Metroid was the winner that weak, and sold more copies than Bioshock in the same weak. I have no clue about Bioshock's 2nd week number. But it's not gonna be anywhere near the 400.000 first week's sales! So it's a bit premature to say Metroid sold more than 400.000 units. I'm hoping it will though.
