Well, the main reason is for the exclusives. But, I think Brand loyalty plays a smaller factor. I have had every Playstation console. I like Playstation consoles. They are good systems with good games.
Oh, I bought a Xbox way back in the day. The only games I could play on it and not my PS2 were KOTOR and KOTOR2. Those were literally the only games I think I ever played on the system. The result is that I love KOTOR and hated the Xbox. Thus, since the games sucked on the original, why would I pick up the sequel?
So, in an odd way, a bad experience tainted my views of a console so that I don't like it's follow ups that much. Though, I respect the 360 for what it did right. Still had no games that I wanted...
And that's a major reason for me to get the PS4. A variety of good games. Games that look different from each other and have colors. Games that I want to play. And PS+ certainly sweetens the deal with free games.
All Xbox One has is Titanfall. I might have picked Titanfall up on PS4, but I won't buy a Xbox to play it. So, EA lost one sale already.
*Launch titles are barely a thing. I'm not looking forward to any launch titles, but Infamous 3 and Destiny are already preordered.
*Backwards compatibility is nice, but not deal breaking.
*Multiplayer is nice for multiplayer games, but I think both systems do that pretty well, now.
*Hardware specs has always been a sort of "lowest common denominator" sort of deal. When making a multiplatform game, they tend to make the game to play on the weakest system. So, it doesn't matter as much, though I still note it.
That pretty much sums up my views, I think.