if you were 30 minutes late to a doctors appointment...

Would you expect to be seen immediately when you came in? Given that you didn't call to move the appointment or give them a heads up that you're going to be late? The lady came in on her high horse at 12:10pm like 'But I had an 11:40 appointment?' Okay but where were you at 11:40? (the doctor actually called her in at 11:41).
I'm currently at work and this seems to happen a lot. Patients miss their appointments then wonder why they're being made to wait? I don't understand? Am I missing something here? You missed your appointment but you can't figure out why you have to wait till the doctor is free?