Well firstly - about Jan sales, there was a massive PS3 shipment on Dec 31st and you have to remember that Wii and PS3 sales in Nov / Dec are purely a function of availability. Demand is there (for Wii especially) to sell plenty more. If Nintendo could ship 500,000 in Jan they could probably sell them. It is not unreasonable to think Wii and maybe PS3 will outsell 360 in the next couple of months as supply catches up with demand. This may have already happened with PS3 but Wii is certainly sold out everywhere still.
Secondly, the shipment / sold thing again. PSP shipment figures from Sony for a long time were much higher than DS shipments even though DS was outselling it in every region (albeit only by a small amount in the early days).
Everyone suddenly started claiming massive PSP sales in Korea, China, Mexico - contrary to all logic and reasoning - in an attempt to consolidate PSP shipped and sold figures.
Now that DS is absolutely thrashing PSP in every region the argument has died down, but still you have PSP shipments of nearly 30m (vs 35m for DS) compared to sales of barely over 20m (vs 35m for DS - sold out everywhere), what is going on there? Is every tracking service in every region in the world massively underestimating PSP sales and getting DS spot on?
Same thing seems to be happening with X360.
There is no way you can get close to 10 million without making some crazy claim about Korea, China, Mexico etc being massive "unaccounted for" regions. If this was the case then surely we wouldn't be able to match up DS sales so well to shipments?
This whole thing is estimates. NPD make estimates based on a (large) sample, Media Create, Dengeki, Chart Track, Famitsu, GFK all do the same. We take base estimates, shipments, projections, use historical trends and so on to come up with our overall estimates.
They are never going to be 100% perfect - it is impossible to ever know exactly how many of a console / game have been sold, but we constantly re-assess and readjust in light of new data and info, and strive to make sure the figures are as accurate as possible.