I certainly agree with your logic, Fred. That's why I also chose F100 over F5, D100 over D1x, and D700 over D3 (although I did do 4 trips with the D3 before the D700 was available). My exception was D2X over D200, mainly because the D200 had a significantly poorer sensor and much poorer AF.
That said, I think that the housing makers have been a little surprised how soon the D800 arrived and the delay on the D4 closed that gap further. But I based my expectations on the fact that most started work on the D4 housings as soon as it was announced in January and therefore projects were well advanced before the D800 became a reality (despite the fact some of us were already using it - I didn't tell any housing manufacturers about it until it was officially announced). But I don't doubt that for a moment that the D800 is the far more important camera for underwater photographers.
It will also be fascinating to review - to see how much of the resolution can be realised in wide angle and whether switching to DX mode is a huge benefit or just a frustration that you are throwing away 2/3s of your resolution. I honestly don't have a clue to the answers - and I think that is very exciting!
Alex