It's no secret stadiums are cozier, with fans closer to the action.  That perception is accompanied by the  realization that a  decrease in foul area has occurred as well.  Could the decrease in foul area have affected SO? Stadium diagrams were downloaded, with permission at www.andrewclem.com, and foul areas determined for AL stadiums from 1954-2000.   Average stadium foul area was determined for each year (left y-axis), and graphed against SO/ Sq. Ft. Foul area (right y-axis).  Average foul area decreased approximately 14 % (31,800 to 27,300 sq. ft.) from '54 to 2000.  The most notable separation of the graph  lines occurs in the 90's, where average foul area dropped approximately 10%, while SO continued an upward trend already initiated in the 80's in the setting of stable foul area.  The relationship of the decrease in foul area with a dramatic increase in SO in the 90's is certainly notable, demanding further investigation of the potential effect of foul area on SO.

Acknowledegements: www.andrewclem.com, baseball-reference.com