When i check they are the same.

To further complicate the issue, Amazon did not have a lot of the better offers of brick and mortar retailers and does not make up for the majority of consol sales. 

But seeing that now this virtual stores have better deals than b&m things will be harder to measure.

How does the fullfilment works? Amazon sells for 399 but is fullfiling a 339 offer, where is this stock? How much will the vendor receive for the sale?

I really don't know how Amazon do their stuff, but what I can take from it is.
They consider the Month as a period of time, so 30 days and not it's over as a new one begins, so by now XBO numbers are still inflated there by how much they were selling still in middle December and over.
And the fact that even the PS4 winning the weekly both just went down in ranks, is that the demand for them are not high compared with other products that are rising now, as the PSN cards, so even if the PS4 is having more sales than the ONE it can still take some time until it surpasses something between then or the XBO fall behind it.
We will probably only have a good idea of how are things going with the weekly this month until some more days or when it's really in the end of the month.
As of now, PS4 is selling more in January already as the weekly tell us. And as it's doing it in the hourly as well since a good time, the XBO probably won't catch up to it and it'll probably take November NPD, that is, if Amazon still keep doing it's good job to tell us who will lead with their ranks.