1D Mk2 also has a new flash exposure system (ETTL2). So now that ETTL has been almost worked out, the housing manufacturers can start working on a new puzzle!
The 1Ds certainly has some advantages, but with the current pricing and the numerous advantages the 1DMk2 has over it's older sibling, I can't see many people buying a 1Ds now.
In the Canon white paper I linked to above, Canon explains how kind they've been as this camera is worth $6000!!! According to them, they're letting you have it at a bargain price! :?
In terms of their kind consideration for underwater photographers, that line isn't official Canon PR spin. It comes from their USA technical director, who makes a lot of useful posts on Galbraith's site in a semi-official capacity. He tends not to indulge in PR spin, and he's responding to a group who really couldn't give a toss about underwater photography anyway, so I think it stands as an interesting comment. FWIW, if this is Canon's design philosophy your 1Ds/1D Mk2 housing is likely to have a bit more longevity, which is probably a good thing given the prices being bandied around here for 1Ds housings!