Someone posted this in the Talk page:
This website is well-known within the gaming community for fabricating sales numbers. It is not known by what method the site's operators conduct their sales research, or indeed whether they even conduct any research at all. Their numbers are just as likely to be right as anyone else's guess. However, large media outlets such as the New York Times apparently have quoted their numbers in the absence of credible sources of information, leading to the impression that they are a legitimate market research organization. The fact that most video game enthusiasts do not believe their numbers carry any weight at all should be reflected in the article. Let me clarify that I believe that although the site claims to perform research such as tracking sales data at retailers, these claims are just false. Their numbers are often off by huge margins (i.e. 100% or more). Only one person is known to be responsible for the site's numbers - its owner - and he has no credentials except being a gamer who follows sales numbers.
We can easily use the March NPD numbers to prove him wrong.