In general, the "let people off before you board" rule is an excellent one, and it should be extended to all elevators as well. (I'm astonished at how often I'm in an elevator that opens to someone charging into the car with apparently no conception that someone may want to get out.)
But be warned that I don't wait patiently for people to exit if they are:
• Chatting or texting on the phone as they make their way to the door, under the totally mistaken impression that they are doing two things well at once.
• Gathering up the half-dozen shopping bags or suitcases that they spread out as if they were making themselves comfortable for a four-hour Amtrak ride rather than a four-minute subway trip.
• Eating or drinking anything, especially if they take a moment to stuff trash under the seat.
• A group of students or tourists who refuse to step off the train individually, instead waiting until everyone is in position for a Rockettes-style synchronized exit.
If you fall into any of these categories, I may brush past you and even smirk if the doors close before you can get out.