I would say its multiple things. First I would say its games. There are people expecting another God of War, Gran Turismo, and new franchises like Bloodborne and the unveil of Uncharted 4 help push continue PS4's momentum. It was genius of them to really be aggressive by courting indie developers. It always feels like something is coming out on the PS4.
Microsoft's PR debacle effected people's decision. I remember awhile back after months being out, a casual gamer asked me if you have to always be online still to play video games on the XB1.
Sony is a stronger gaming brand. The PS3 catching up in sales of the 360 pretty much proves that. I think it was going to good regardless. They have a good reputation and ended or ending strong with the PS3 with The Last of Us, Puppeteer, and Beyond Two Souls.
Sony started out cheaper and had a clear message and stuck to it.
I think it is a bit of everything. I think Sony has done a great job and they will hold the lead the whole cycle but I would expect Microsoft to at least have some bursts of momentum from various games. I hope if anything this will keep Microsoft from relying so heavily on Halo, Gears, and Forza. They need to stir the pot with new titles that could sale the XB1 to people outside their typical fans. I don't want this to be a completely one-sided win.
That is my take on the subject :)