Dean:

If you think about it, something like a simple 43mm lens, which has a nodal point in the middle of a single element, would have to be only 43mm away from the film in order to focus to infinity. That would get awfully close to the moving mirror in a medium format SLR.

For that reason, those who design lenses for SLRs are forced to make them retrofocus type lenses - which means that the glass elements in those lenses are actually ahead of the nodal point in the lens. Retrofocus lenses force the lens designers to make some serious compromises.

In comparison, a rangefinder body is much easier to design for, because there is no mirror in the way.