Nintendo claimed they were shipping 1.8 Million Wiis a month (soon to be even more). According to this site it sells about 400k worldwide every week. Assuming Wiis are flying off the shelves what accounts for the discrepency?

Nintendo holding back supply and then supplying areas when needed at times of big releases (Wii Fit, Mario Kart, Brawl, etc.)

general stockpiling. If they sold at a contant rate, then what happens when christmas comes and you don't have any more? Nintendo stockpiles for christmas and other big events such as big game releases in which sales sky rocket to well over 400k a week.

They stockpile for when GTAs, FFs, GT5 and such come out. Then they release enourmous amounts, and a Nintendo game, to counter and take attention away from the HD.

Christmas 2008 they're gonna sell about 10 billion and reveal the doomsday device hidden in every Wii (and now in every home).

400 times 4 = 1600.

1 month is arguably 4.5 weeks, 1600 + 400/2 = 1800.

What discrepancy?

Simple:

Consoles sell at a different pace at different times of the year.  It takes about 3-4 months depending on your situation to go from the decision to increase production to the actual increase taking effect fully.  So you can either raise and lower production throughout the year spending money on stuff to handle the logistics of the affair or you can set one steady rate of production that will allow you to build up surplus for the periods of rapid sales.

This is the default stockpiling that happens in every company and many don't believe it happens at Nintendo because of Reggie's comment that it doesn't.  The problem with this of course is that in December of 2007 there were nearly 4.3 million Wii sold.  This of course requires us to ask..ok then so where did the other 2.5 million units come from?  The answer is of course stockpiling. 

ninty isn't shipping 1.8 mil. they're MAKING 1.8 mil per month. there's a huge difference.

400 000 a week is 20 800 000 a year
1800 000 a month is 21 600 000 a year

Huge discrepancy