Possible reasons:

1.  Economic:  You can maximize interior (leasable) space by pushing the enclosing (non-structural) exterior wall out to the face of the structural columns (or even beyond, if floor and roof beams cantilever beyond peripheral columns).

2.  Aesthetic:  Exterior walls centered on the column grid don't conceal the columns, generally.  Modernists are usually fine with that arrangement because it allows them to highlight the structural elements on the exterior facades.  Others, however, want a more finished and uniform surface that a continuous wall provides.

Okay, there's two for starters.  Next!

3. Climatic: Steel columns work as cold bridges when perforating the outer skin.

4. Detailing: Tolerances for structural members are higher - a steel column might deviate 10mm from the grid, making it difficult to create a tight connection with your facade elements. When exposed to large temperature changes this might become an even bigger problem, of course.

Neat question.

Many framing systems keep the bones of the structure within the skin.  Steel frames and concrete moment frames, to name two.  It comes down to whether you hang the skin on the frame, or the skin is the frame.  

This next comment will highlight my inexperience, but perhaps others can chime in: isn't two stories a bit short to have a structural frame?  Wouldn't a masonry bearing wall make more sense?  (of course the nature of the building program would ultimately decide the most efficient structure).

I would think that in most circumstances the skin would basically lay on the exterior face of the framing system (that's over generalized, but oh well).  So figure out (guess) the width of the columns and use the exterior face as the plane that the interior of the exterior skin lays on.

Check out the "Building Systems" pages in your Arch Graphic Standards book.