Lots of folks expected that we would have heard something about Fallout 4 by now, given Bethesda Game Studio's recent development cycle and the fact that the last thing released for Skyrim had to have been finished by November of 2012. They didn't actually announce they were moving on from Skyrim for another half a year, though.
Could there have been another DLC planned and worked on that they decided to scrap, possibly because the PS3 couldn't handle another one? That might help explain why they aren't far enough along on their current project to have told us anything yet.