I have a few potential reasons why the PS4 is not first. PS4 is more readily available... amazon is no longer the only online retailer with PS4s, and people at GAF are saying B&M stores are starting to get them.
Also, PS owns 7/10 spots in the top 10 and they're all pretty much helping each other. The camera could also crack the top 10. PS cards are probably being purchased more than before with hardware sales going up, and quality software coming out.
Like I have said before, amazon's rankings are no indicator of sales rate because there are several factors that can cause their rankings to change in a given month or week.
Also, FWIW, famousmortimer at GAF said to not sleep on Infamous... sales between Infamous and Titanfall are very close. Not sure if he meant in the US only or worldwide. If he meant the US only, I'll be surprised... I thought Titanfall would comfortably outsell Infamous in the US.
Sales #'s are very hard to come by, especially somehow "in progress". Famousmortimer is not a real source. I mean I guess he could be right, possibly as well just by accident/guessing, but there's no reason to really think so. Also if you'll notice pretty much all his info is designed to praise PS and cast aspersions or negative news towards Xbox. Doesn't make it automatically invalid but should be considered.
Just offhand I'd think Infamous has a good shot to beat Titanfall, why not? Both are about equally hyped games in very similar positions. Both consoles sold a bunch, then came a software dry spell, and both are the huge titles slated to end that spell and coming out at a similar time frame in March. I dont see a reason to much favor one or the other. I guess the only caveat is Infamous hasn't been a sales beast before that I know of (it's successful but not a monster) but just by intuition this time is different.