Uau, nice find. Looking at those numbers I get this: the 2005 data is actually pretty good; the 2006 data really seems far off.
| 2005 | VGCharz | AC Nielsen | Difference
|
| DS | 440556 | 425000
| +3.7% |
PSP
| 306228
| 295339 | +3.7% |
As for 2006, Nielsen reports a market split 62-38 in favor of the DS, while VGChartz splits it 49-51 in favor of the PSP. Nintendo themselves also said they sold twice as many DSes as Sony sold PSPs.
If we were to cross Nielsen's and Sony's numbers (which we really shouldn't, because Sony's numbers might be shipments not sales, and might be fiscal not calendar), it would still show an overestimation of the PSP by almost 30% and an underestimation of the DS by more than 25% (which despite being "wrong" says something).
Also according to Nilsen the DS user base in Spain is at over 1.5m. While it isn't clear whether this was in March or December, VGChartz still hasn't reached that number - it's at 1.3m right now.
All this info comes from TheGame's sources, see his post for links.