Just to clarify Yoshida's comment. He is not talking about "hardware" in general (there won't be any change in specs). Adding 4G of gddr5 ram in "the last minute" poses considerable challenges to the case and pcb designers. 32 gddr5 chips, that is a lot of real estate to account for, and thermal dissipation problems just went up a notch or two. Internal or external power brick probably hasn't been decided yet I'd guess.
It was clear that Sony wouldn't show the PS4 box (and why should they? Do people really want to look at a piece of plastic instead of people showing off what can be done with the plastic box?)







