At the current rate of sales, for Nintendo to approach a near 100% sell through, they absolutely will have to have at least a 4 week period (from Black Friday through Christmas) in which they average or exceed 1 million consoles sold per week.
I believe 4m+ sales for the peak month of the year is extremely within the realm of the possible.
As for the yearly prediction, it is fairly simple. Production was reported by Nintendo as increasing to 2.4m/month as of July, which means they have the capacity to produce no more than 14.4m consoles over that six month period through year's end. Sales as of the first week of July were well under 30 million. I believe it was about 28.5 million, according to VGC.
What this means if those numbers are correct, is that over 45 million in retail sales by year's end is very unlikely unless Nintendo had at least 2 million consoles in warehouses on hold. Not impossible, but to believe Nintendo has 17 million consoles (for a round 60m by end of 2008) sitting quietly for the time in which they plan on carpet bombing retail outlets with that much unsold stock goes beyond unrealistic. No one, not even Nintendo's own accountants would project this.
Production has been increased every six months; 3.0m/month in Q1 2009 is very likely (early as January) depending on how well console sales are. If they do as well as last year, it's guaranteed. 4.0m/month is highly unlikely, until the back end of 2009, if such a production increase is made at all. If sales drop back down to an average of 350k/week, or even a phenomenal 500k/week, why would Nintendo peg production at 1 million/week?
Until new data and catalysts are present, some times you just have to make a common sense call, and leave the wild predictions to the marketers who are trying to attract investors.