I could easily see the following happen:
360, PS3, Cafe: Developers stick with 360 as the lead primarily, and simply port to the PS3 and Cafe. Maybe a couple of developers want to stick their neck out and develop on the stronger Cafe system, to 'up the ante,' but that's about it.
Cafe, PS4, 720: PS4 and 720 launch. Given that software has sold on Cafe, and it's not massively - MASSIVELY - weaker than the PS4 and 720, why on earth would I (a developer) increase my costs on the new systems and make porting to Cafe impossible? Why, in essence, would I cut from selling on 3 platforms down to 2 as I increase costs? And if I do that, doesn't it sort of show that I learned nothing from the Wii, 360, PS3 generation?