I agree the E-3 and the D700 are not really comparable, it would be fairer to compare the D700 with the D3 or the 5D or the A900.
One thing should however not be forgotten. With an FF, not just the D700, there comes a time when the narrow DOF is not wanted and one wants the same DOF or more than the Oly 50/2 can provide at f/2. Here comes a small problem. As soon as you want the same FOV and DOF and exposure you must increase the ISO quite considerably. So it is only natural that Nikon and other FF manufacturers needed to produce better high ISO capabilities or else nobody would pay the price of those cameras. An example:
If you use the E-3 with the 50/2 @ f/2.0, 1/125s and ISO 400 then the D700 must use a 100mm lens at f/4 and ISO 1600 to get 1/125s and the same DOF and exposure. That is even worse if I need to use ISO 800, which is still very good in the E-3 because in that case the D700 must be used at ISO 3200 which is no longer as nice as ISO 800 in the E-3. Even the lack of in body IS in the D700 is something which may call for higher ISO than necessary, unless the user has the more expensive VR lenses. So, while there are advantages of both systems, there is definitely a flipside of the high ISO advantages as well, since as I see it, it is really a necessity in every FF.