It's a two pronged deal. One, it keeps the crippled folks out of the emergency exit row, two it preserves the EE row as an option for the guys that either paid for or was awarded A1-15.
The bad part is that it restricts JSers who preboard from sitting there. They are arguably the most capable and well trained people in the plane and the folks that I personally want there.
You honestly lucked out that the ops agent let your wife preboard. They did you a solid. My wife doesn't get to preboard with me usually, and I work there.