At least that's not a universal truth. It only applies to cake. You CAN have your beer and drink it too!Can you imagine how injured a person would get going around telling people, especially in TEST:
"You cannot have your beer and drink it too."
You can buy a 24 pack of beer and people will be happy. Buy 24 cakes and you'll be arrested for creating a cake shortage.
You could buy cup cakes but that's like buying beer shots. No one wants 1oz of beer. Give us a the whole took (beer bottle)!