Posh names for simple meat

Why do we eat beef, mutton and pork but the actual animals are called cow, sheep and pig. The differentiation dates from the Norman invasion. 

The peasant spoke the Anglo-saxon common language where animal and meal were called the same way: cow, sheep,pig... 

The upper classes, who had enough money to eat the meat, wanted to sound fancy and agreeable to  the conqueror by using his language (French) to describe what they were eating: beef from the french boeuf, mutton from mouton and pork from porc.  

 Nevertheless for the less expensive meat that could be also eaten by the less fortunate, the name remained unchanged (e.g. Chicken) and is just as tasty!