Personally I think it's context. X1 did shockingly well consider.
-All the huge launch negativity/DRM
-Tons of rumors of catastrophic yields
-$100 higher price point (this one is huge)
-Apparently weaker hardware
-Moar Kinect hate/backlash
I mean we heard rumors of 4:1 in USA and 8:1 in EU, PS4>X1 supply a few months ago. Reality is nothing close to that.
Edit: I forgot we even had Pachter predicting PS4>X1 by 66% a few days ago too (1.25 vs 750k).
Further signs look good that One can take Dec NPD, which means that as of Jan 1 X1 can be ahead in the USA, which truly I think is kind of amazing given all the obstacles. Also you have the fact hardware revenue was roughly the same between PS4/X1 given the X1's higher price.
Even worldwide, say Sony is up to ~3m now (which is generous), that still only gives them a 3:2 worldwide advantage on X1, and again given all the negatives above that's impressive. The key for X1 will be securing enough install base that 3rd party support is secure throughout the gen, and the early going looks very good for that. Publishers wont be ignoring 2+million consoles already out there.
And if you compare it to PS3 v 360 it's also excellent. MS had every right to get blown away considering PS3 was facing a year deficit and a 599 price tag. Now PS4 has the advantage in price, and is launching at the same time, yet Xbox still did fairly well.
Going forward, it depends when MS wants to do a price drop to 399. If we assume they do it in late 14, then you can look at most of 2014 as a holding action to not fall too far behind. For Sony it will be about how much supply they can get out there and how much demand remains in spring.