You've made me quite curious now. I thought boxes at the side was the normal pattern. Boxes in the middle above the stalls is not a pattern I've seen. I wonder if it differs by country and age of the theatre.
At least that's the oral tradition I've been given in the UK. Makes sense for the old aristocracy, the US may have wanted to make a deliberate break with the tradition?
In the monarchical period of European theatre, it was well-understood that the centre was a _pit_ full of hard-scrabble riff-raff. Having a box apart from this was a sign of social class (i.e. _wealth_ and aristocratic connexions).