There are more than 4 weeks in an average months (about 4.33) so the weekly production is more like 413k than 450k and the latter would be about 1.95M a month.
That being said, while I believe the Wii may achieve that this year it is far from certain due to both other consoles doing better (lower price points) than last and capacity to improve (plenty of great games that should boost sales and possibility of further price cuts).
Even if it does it probably would lose it around the holiday season as the other two combined would outsell it and I find it unlikely that the Wii would have a big enough lead over them (combined of course) to keep 50% marketshare.
If it does this year then cool but if it doesn't it definitely will in 2009.
Sri Lumpa here, I lost the space when I lost my profile 
