personally, I'd be amazed if we don't at least see the next xbox and playstation announced at next years E3. They probably won't ship very soon after, but another year only on PS3 and xbox will garner such a negative response I think it would damage them permanently.
I'd expect the xbox to ship worldwide at the same time but in contrast I think Sony mights tick to their habit of staggering launches around the world. Next Xbox for christmas 2013 everywhere, next playstation same time in the US but maybe the March after in the EU.
They just can't say when they're going to launch, because if they say they're going to launch next christmas, they'll kill their sales this christmas. So they have to do the reveal in the same calendar year as they ship. And they're (I assume) not ready for this christmas, so...
Jon