In my dream world, I say that Canon and Nikon are delaying their respective releases because the next generation of APS-C sensors are so good that they don't want them on the market until the 6D and D600 have had time to turn a profit.
But D300 / 7D are cashcows in the higher Crop segments. So, some persons think, that the first company that releases an successor, will have better chances on the market.
Nikon rented some D800E for an landscape workshop, I visited. The Nikon specialist & workshop director told all Nikon fans, that there will be an release of an new D300 in the next month. Only a little bit delayed by an new invention of an anti-dust management. (He told there will be a solution for the D600 problem (seems to have an problem with dust on the sensor).
So Canon will/should hurry up.