They still sell ps2's, and there's still the odd game that gets release for them, and the ps3 has been out for about 5 years now?
Sony doesn't drop support of their previous console when a new one comes out (ahem microsoft!). So there's no reason they can't release asap, and still support the ps3.
But now that the rumor mill is going, MS will ramp up the new xbox as well. I think Microsoft had a huge advantage coming out first this time... they might want to repeat that success.