As a huge Nintendo fan, and someone who thinks we'll have a big holiday, I'm asking the same question. Only if Nintendo is holding a decent exclusive up their sleeve (along with a price cut) do I think they'll achieve those numbers. It's just hard to imagine they'll move 18 million consoles in 9 months.
I they said they'll get 16 million again this year, I wouldn't have batted an eye. 20 million, though... We'll have to see.
Retro Tech Select - My Youtube channel. Covers throwback consumer electronics with a focus on "vid'ya games."