PC to PS4 ports take weeks, not months
PS4 lead system architect Mark Cerny gave Gamasutra the full rundown on the upcoming system's hardware specs. During that talk, he very lightly touched on what we can expect for the PS4 launch.
Though he couldn't give a title count, Cerny said that the launch lineup for PlayStation 4 is "going to be stronger than any prior PlayStation hardware." This statement comes after his explanation of his design philosophy for the system, which focuses on both power and familiarity in what he calls a "supercharged PC architecture."
Cerny goes on to say that the launch will be strong as a result of familiarity. He noted that it takes "weeks, not months" to port a game engine from the PC to the PS4.
That said, Cerny looks forward to the future as developers grasp the capabilities of the PS4, so that they can customize their technology and "really reap the benefits."
If you're interested in the period beyond the launch window, the Gamasutra interview goes into how Cerny believes the PS4 tech is future-proof.