The Nehalem doesn't neccessarily have to be at the very end of 09 at all, it could easily be at the back end of Summer or beginning of Autumn.
The prediction might not be that far off, without switching up the CPU's for an entirely different architecture they don't have much left to do with the current model.
This was discussed before, it's entirely possible Apple will hold out, and every Event and Tuesday that passes before that point just fuels the fire.