Close coupling is another technique employed to give scale models a more realistic appearance. Like all of these techniques, using scale or semi-scale wheels, weathering, etc... it is a matter of personal preference. For those who prefer, this is what I do.
When I build a car from scratch, close coupling is a natural benifit of the design. By mouning the draft gear close to the end of the car and using a short shank coupler, close coupling is automatically achieved. When it comes to commercially produced models, there is a little re-engineering involved.
For a more scientific study of this subject check out this interesting and in depth article from Budb.