1UP- The NPD Group's monthly games industry reports continue to be widely covered in the media, and it's easy to understand why. With game publishers hesitant to make a habit of sharing sales figures, the NPDs, as they're often called, supposedly give us somewhat of a glimpse as to which games are succeeding and which are failing. Criticisms of the NPD Group's numbers have becoming increasingly common over time, to the point where the question is now being asked whether the media ought to ignore the numbers outright.
20°
10°
20°
30°
Ad 
40°
NPD numbers do not draw any kind of picture at all. There is no problem with them as they have been doing the same thing for years.
The problem and the "incomplete picture" are derived by those who try to perceive them in their own fashion. As a marketing tool they are meant to give a representation back to the companies. NOT the consumers.
Its like trying to understand Nielsen Ratings. The ratings number essentially are worthless to us as viewers even though we can ascertain low numbers mean a canceled show in the future. Its how those numbers are really viewed and studied from the network side that means the most.
As for NPD and other number gathering groups in the game industry, someone thought it would be a neat idea if we (gamers) saw them but never really told us the best way to understand them. We assume that the numbers are taking an obvious position in that high numbers are good and low numbers are bad. Yet we are so narrow of view of the broader spectrum that the companies see.
I think we should stop trying to relate these numbers to anything that is for or against our individual agendas and just play the god damn games.
But the real problem with npd sales are the fanboys you see on NeoGAF and vgcharts. Their egos rise and fall on this data, and most of them use it to justify or express their hatred for rival systems / companies. And hey, when the numbers don't go your way you can always hide them like they do on NeoGAF. (Even though their source receives the full numbers every single month.)
Quite simply, sales nerds aren't real gamers. In before the "but I wanna work in the industry" excuse.