Title says it all really. I dont understand how this site can have a lower number than media crate by such a wide margin unless they have made an error when inputting the figures? I have checked other sites and they all report the media crate numbers so what gives?

30K isn't really that much off. Now if it was 3 million off that would be a different story. With the 3DS selling around 170k or so a week that would be like being a day off.

Yeah. it's not a big deal unless it's Vita numbers.

I disagree its a pretty big gap considering they pretty much have the same numbers as media crate for all the other consles. Are they saying media crate are wrong?

Numbers will never match other sites unless they adjust them. Basically, VGC is an educated guess with some research. They try to track as much as they can with their resources but it will never completely match the released results from other research groups/sites , the big 3 reports, etc. I believe they usually wait til NPD numbers and then make adjustments then. Someone else probably knows more about how everything is done but you can't expect perfection with this site.

Margin of error?

Because no system is perfect, and they reserve the right for a margin of error.

Plus, there have been bigger discrepancies from time to time...

Because VGChates Nintendo, obviously.