I personally come from work most of the time when I go and see a show, and in theatrical offices, a large number of us wear jeans and nicer tops (I usually rock the blouse/cardigan combo). Since I get off work a 6, it is impossible to run home and change for a 7:00 curtain (or sometimes even an 8 if the MTA is feeling particularly helpful). Yet, the fact that I am wearing appropriate attire for work seems to be lost on a few patrons now and then when I sit next to them in the orchestra and they are wearing the dresses and spanks.
However, when I go home and see a show with my parents (I too am from Houston), or even if I go back to the Chicago/Indy area where I did my undergrad, you can bet your butt I dress up a little more (usually I swap the jeans for slacks and the cardigan for a blazer - very rarely do a wear a dress).
For some people, Broadway is their first theatre experience because "it's the thing to do" and they just might not realize that it ISN'T like a movie theater.