Their numbers are completely different than those of vgchartz. There is a huge difference.
Wii :
Nexgenwars : 13 millions
VGchartz : 18.5 millions
360:
Nexgenwars : 12.5 millions
VGchartz : 15.5 millions
PS3:
Nexgenwars : 5.5 millions
VGchartz : 8.5 millions
To me it's obvious that nexgenwars.com is a joke site. They probably get their numbers out of their asses.