It must be tough for Nikon, in today's hyper-competitive business world. I believe their senior executives recognise the challenge and are working on faster iterative ability. One of their top brass (president?) made a public statement last year about the need to produce new models more quickly.
Of course the speed of iteration tends to be quickest at the bottom of the line and unfortunately slowest at the top. Sheesh, given the release of the Sony A77 yesterday (and the 7D a couple years back), Nikon had best be coming with a great D400. I trust they will.
I'd have to say I agree that at the D300 and D700 level of the line up, Nikon will have to increase their speed of iteration. It is simply too competitive out there!