Show me the equation, I haven't found it through a quick google but you know where it is so make it easy for me.
I don't wonder, it's because NPD's numbers are more accurate, which I never questioned. What I question is your claim that NPD uses estimates while VGC uses guesses from a hat. Both use estimates, it's a question of degrees of estimate and accuracy, which can be debated.
I do. If Media Create and Famitsu can publicly release their numbers on a weekly basis then there's no reason at all NPD couldn't be doing the same.
There's an wasy answer to that question - there are two pretty accurate Japanese trackers. There aren't two pretty accurate US trackers. There is only NPD.