It's my opinion that if a child throws tantrums at home but behaves appropriately outside the home, then he's just testing boundaries at home and you are responding appropriately. If he throws tantrums outside the home but not at home then it's more manipulative behavior and he knows how to work you, and get his own way-- not a good thing!
I like Alines comment about the grown-up conspiracy! I don't agree with the current philosophy that 'no one disciplines my kid but me'. There are too many kids with no respect for authority of any kind.