When you look at the stats of the D700 (287 cameras in the D700 database) he's showing the average number of actuations after which the D700 died at 149,666, yet it's also showing about 17% go on well past that number.
There is no doubt my older D700, now my backup is on borrowed time. I certainly could invest in a new shutter for it, but I'm not sure that makes a lot of sense at this point.
I really can't afford to travel without a reliable backup, so the new camera is an important purchase.
For those who think a backup camera isn't important if you're shooting something or someone for which another opportunity might never occur, or you're being paid to get the shot, let me pass two stories along.
I was in a workshop with Joe McNally about studio lighting. I was there to get ideas, and learn more about portable studio lighting from a practical standpoint. (The workshop was great, by the way.) Joe was using his D3s for the workshop and before the morning was over, it died. Halfway through the afternoon another D3s died. Fortunately, he actually had 3 (possibly 4, I don't remember) D3s cameras, so the workshop continued.
Later this year I'll be shooting in Antarctica. There are no repair shops or stores there to get my equipment fixed or purchase anew. I'll probably never get back there. It's worth it to have a reliable backup, even if you've got to rent.
I know a birder who's at a local wildlife refuge about as much as I am. We were talking a couple of months ago about the Galapagos. He wanted to know what equipment I've used there. During the conversation I suggested he should have a backup camera as he'll likely never get back there. He had his regular Canon DSLR (No boos, please - he's otherwise a good guy - LOL.) but not even an old camera he didn't use any more. He took my advice for this trip and got a rental. When he got back he told me he wants to take me out to dinner. His camera broke 4 days into the trip, but the rental worked perfectly.