Before you assume FFXIII is on the order of 3x larger than NSMB Wii based on Comgnet (which it isn't), remember that sales/preorders vary tremendouly by platform at retailers.
In the USA for instance DS may perform best at Walmart, Toys R US and Target, while PS3 performs best at Best Buy, Game Stop, and Walmart.
So if Walmart was little you might see:
DS - 5,000
PS3 - 500
That doesn't make DS bigger than PS3 at a 10 fold ratio even if this miniature Walmart has substantial marketshare.
People are difficult to govern because they have too much knowledge.
When there are more laws, there are more criminals.
- Lao Tzu