Are there any technical reasons why Nikon would have done this?
Nikon did the right thing; they store the correct camera model in the Model tag. No "evil" intent.
It's the raw readers that are fussy. No one can know ahead of time what new models will come out and whether parts of the file format might change with a new model. So most readers simply fail when a new camera comes out until there is a revision to support the camera. It's a safer approach then having a bunch of people complain that their raw software is buggy when it was never developed or tested with that model of camera.
What makes Nikon's software policy look a little bit more cynical is that they released a Capture NX 1.x update very recently (more recently than the View NX update that added D700 support), and chose not to support the D700, even though it would obviously have been trivial for them to do so. This was pretty clearly a marketing rather than a technical decision, neatly taking advantage of the (expected and perfectly valid) change in the Model tag.
In addition I am pretty sure that Capture NX development is done in San Diego by Nik Software. As a developer who has been involved in joint venture spec creation it is likely that the specs for NX have been in the works for many many months.
Though of course Nik have also been developing NX2 (which does have D700 support) for some time as well, so they obviously had access to the D700 NEF specs if they'd wanted (or been allowed) to use them. And how many lines of code would it really take to add D700 support to a raw converter that already supports the D3? Nikon did exactly the same thing when NX1 replaced Capture 4.x (4.x supports the D2X, but D2Xs support was never added). My guess is that it's Nikon policy never to add support for a newer camera to older versions of Capture once a paid upgrade (like NX2) has gone on sale. We might get bug fixes and even minor new features (like we just did with NX1), but that's it. Adobe does exactly the same thing with PS/ACR, but they do at least provide a free DNG converter that lets you work around this.