What a crazy story. Sounds like the usher told the lady to sit down there, then the other lady freaked out and threw her out of the seat. So I don't really feel sorry about her getting a ticket. Its not all that strange for a theatre to have a seating policy either, I've seen that alot. Sometimes its that you can only save one seat, or only save seats that you are holding the tickets for, or only save them until the show starts, etc. But usually when they are planning on enforcing them, there are signs posted up in line and when you walk into the theatre and such... no idea how visibly they had their policy posted at that theatre. Also, I generally see people being pretty friendly and people switching seats and different things so at least two people in a group can sit together. It kinda sucks to be stuck in a corner by yourself.
I don't really have a problem with someone saving a seat or two, even if it means I get a crappy one. The most uncomfortable I ever was at a movie, I got stuck in this seat that was meant for two people. Then about 10 minutes into the movie some guy came and sat down in the other half, which was alright since the movie was sold out. But then I started to realise the guy was gay, and he started leaning on my shoulder. I would have much rather gotten a bad seat from some punk saving half a row then have went through that, heh.