Have to say, Sony has been really good at keeping people off their guard and unsure as of late. Not sure that is working out for them very well, but at least they're managing to keep a little bit of mystery around this.
However, I still believe that they would not be foolish enough to lapse straight into streamed gaming. There's going to be a PS4 because nobody is stupid enough to leap into the streamed game world and to ignore the use of physical discs and content providers like Steam and PSN where you can actually own a digital copy of the game. Digital gaming is STILL behind physical media, even though its growing quickly, but the concept of streaming gaming is more controversial. Never own another game, never have the ability to use mods (because it's all on their end), never be without your monthly fee for being able to play said games...to say that it isn't a pleasant idea to many gamers would be an understatement.
Though this isn't even about the gamers. It's about shareholders. How many of the people putting money into the company are going to continue to do so when lots of them don't even believe Kaz NOW when he says that the belt will be tightened and hard decisions will be made? "We're going to change to a gaming system that is still in its relatively early stages and won't let our customers actually buy or own their games, but we've got a really good idea that this might be where gaming is going! Maybe!" Try and pitch that to people who you're trying to get money out of.