Because I want the most powerful console hardware for my money.
I had a 360 since launch until earlier this year and it was great until the exclusives dried up about two years ago. I got a PS3 Super Slim this year and the value from PSPlus is outstanding, making me sign up until 2015. I want this great value to continue on the most powerful hardware which is why I chose the PS4 over the Xboner.
For the record I've bought every single console since the SNES on release day. The Xboner is the first one since then I will not be buying at launch.
[1:04pm] <R33P3R> how can a game be epic on a phone?