60 million, huh? You don't need to argue that there is sufficient demand to sell 45 million more units, I think that is obvious. Hell, if 45 million Wiis were to find their way onto the shelves today, they would be sold by Christmas.
Supply is the only thing holding the Wii from selling 60 million in 2008. Assuming they will sell 20 million by the end of 2007 (which looks like they will, or at least close), they will have to DOUBLE production in 2008 to get to 60 million.
That doesn't just mean that they will have to find a way to double their production capacities... since they will have to ramp up production over the year, they won't be producing twice as many Wiis in January 2008. January will see similar production rates to now. That means they will have to make up for that in the later months, meaning they may have to TRIPLE their production rates by the end of the year to produce 40 million.
I can buy that they can double production by late 2008, but that would only amount to another 25-30 million over the year, making 45-50 million units sold by the end of 2008. I will go high and say 50 million.