If Microsoft reveals their next console this fall, it could hurt 360's holiday sales. And it definitely would affect 360's 2013 sales. Just look at what happened to Wii's sales after Wii U was revealed. I have no doubt that 360 will outsell PS3 this holiday no matter what the situation is, but the gap will be smaller if Microsoft's next console gets revealed.
I think Sony has made it pretty clear that they won't be releasing a new console any time soon. PS3 has tons of potentially great exclusives next year (The Last of Us, GoW: Ascension, and Beyond: Two Souls), and Sony keeps saying that they'll continue to support PS3 until 2015. As a result, I think Sony fanboys will finally get their wish in 2013: PS3 finally outselling 360.
As a 360 fan, I'm ready to move on to Xbox 720 after Halo 4. As a PS3 fan, I'm not yet ready for PS4.
P.S. I'm trying to be neutral here. It's not my intention to piss off either Microsoft or Sony fanboys.
