For some odd reason the majority of developers/publishers and other groups will not support vgchartz due to the numbers being made up. Educated guesses or not, most cannot get over that fact. I would assume valve probably has a lot of disrespect for VGChartz.
Giantbomb had no issues getting steam linking, which is kind of unfair. VGChartz is a much better community and I feel that their charts, while never to be taken very seriously provide an excellent comparison factor and should be treated the same as NPD etc.
I had an experience when using vgchartz as a reference on the atlus forums and I was banned for using it by atlusaram, the main communitymanager with something like the sales numbers of vgchartz are nothing less than completely inadequate to compare sales of our games with. and that I was providing false information about the success or no success of their titles to their community.
Essay Pro