Compared to VGC:
Ofc PS4 still has units in transition and on shelves so i think the 2M difference are pretty fine.
Overall VGC has a tendency to overestimate Playstation hardware. And my guess is that its the same for the Vita which sold so bad that Sony does not want to disclose numbers.
This also means that the 3DS still has a shot at overtaking the PSP
And yeah, would be funny if the Wii U actually outsold the Vita in the end but we couldn't confirm it. Maybe it will show up in such a chart later, when it's not being sold for a couple years anymore.
The Nintendo eShop rating Thread: http://gamrconnect.vgchartz.com/thread.php?id=237454