yurtgirl, I totally understand what you did and your reasons behind it. As you keep saying he does not 'know' that it was his b'day, therefore 'his' day hasn't been ruined. As a punishment I am not so sure on the effectiveness, but I can see why you wouldn't feel like spoiling a child who has been acting really badly.
Victoriapeckham I think you are being a bit harsh in your critisism, yurtgirl is not attention seeking, she is trying to canvas opinions on her actions.
Personally I have been tempted to do the same, I certainly threatened to cancel my 5 year olds party, but didn't as it was a joint one with her sister who was 3.
How many of us use 'Be good otherwise Father Christmas won't give you any presents' I remember a whole thread on this one. It that any worse?? That only works if the child can understand it, but I know masses of people who threaten this. OK not many would actually cancel/postpone a birthday, but I can understand why.