Hype.

Since the first Playstation Sony invested in new IP's and thats why the PS4 is doing extremely well in the USA.

1 - Greatest satisfaction on PS3 since it is still supported !
2 - First time in the history you can get the best console for the best price
3 - Genius marketing ( they had to be visionnary to see the potential of the 2 biggest new ip in the history and get a bundle for them on PS4)
4 - Great first party support

Microsoft is the biggest reason for sony's current success. MS made PS4 look amazing in comparison, in reality its actually pretty mediocre. The only other reason is the length between gens was very long so there is pent up demand.

I would say that price and the capitalization of MS's misstakes played a huge part. Also, Sony has a very loyal fanbase and also catered to more fans by releasing in more countries. It helped strengthen the view of them as being for gamers.

Considering that market in shrinking. I think numbers are good.

If one of the new consoles have any chance of at least reaching its predecessor LTD sales is the PS4.

IF Japanese Developers migrate back to the PS4 en masse since it's a Japanese Console and in the process generate enough time and sales of the PS4 for Sony to get their Western studios running again properly, it will do PS2 types of numbers.

Nintendo let the Wii die and Ms was all focused on Kinect,tv,kinect,tv.   Sony on the other hand had TLoU, Gow Ascencion,Beyond and GT6 for PS3 when PS4 had already been announced.

This left a good final impression on consumers about PS3 and Sony in general.

That's why their position is well deserved after all that work on PS3, when the 2 others just let it go waiting for the new generations to come ( it would have been forgivable if they bring more games, but not even close) and i suspect they'll do the same again.

Greatest reason for Sony's success with the PS4 is just so called 'hardcore gamers' are easily falling to the hype. And of course, in the end of last generation most 'hardcore gamers' changed their 'boxes' to 'stations', except for the most diehard fans.