Just like the title says it, I think that Sony is trying hard to reach that number.
I understand the deals on the US to try and match the offers from Xbox One, but they have some insanely crazy deals going out through Europe too, specially in UK. PS4 was still selling amazing good in Europe and in the rest of the world if we are to believe vgchartz. But even then, we are still saying insane deals. So giving Sony's position back in October (before we knew of any price cut from MS for Xbox One), it was more than assured for retailers that they need to stock on the PS4 cause they will just fly away. That put Sony in a position were they could actually afford to "stuff the channels" and give them a lot of those PS4.
Now retailers are posting some good deals out there in both US and Europe. One of sony guys (Can't remember his name) even admitted that sales were a little hurt in the US in november because of the competition.I was even surprise that some retailers even have the PS4 at $350.
I think Sony is really trying to push for that number. Which explain the only PR we had at the Playstation Experience was "fastest selling console of all time", which was by the way a very good news for Sony.