VGChartz actually started on NeoGAF because the founder, ioi, decided that Famitsu/Media-Create/NPD were all under-tracking sales due to a supposed systematic error with their sampling, point of sale, and extrapolation methods. They started producing their own numbers that "corrected" this issue and started advertising their site in those old threads on NeoGAF before getting banned and fully expanding upon the concept.
The issue is that there is no rational methodology behind the numbers produced and shown initially. Then the numbers get updated without documentation to make them look more accurate in retrospect once shipment data and official tracker data is known. It is skeezy and inaccurate.
I don't know much about the community, but they do prop up bad data, so I don't really appreciate that.