Why are U.S Weekly charts Next Gen only ??

[sharky]

What are these weekly sales based on ioi? A couple retail sources or projections based on last month NPD?

 

I'm assuming the the former. However, weren't the vgchartz weekly sales pretty unreliable last month? Didn't Vgchartz have 360 at 337k last month before NPD and then NPD was only 199k?