When I wanted to decide on the brand of the camera to choose between Canon and Nikon, I look at their history too.
When Canon move to EF mount, they make all their existing FD mount lens becomes obsolete and anger many existing users.
Now, when they make EF-S lens, they make sure it cannot be used on EF mount camera.
For Nikon, they make sure most of their lens still works for the current digital camera. The great old manual lens are still trading in the B&S. Nikon make sure your investment is protected.
Although the D700 does not have the megapixel count as compared to the 5D2 but their AF, CLS, Built-in Flash Commander Mode is more important to me.
5D2 is a great camera and I can see many carrying it but to me Nikon is the brand to trust.