Cats have enjoyed milk for eons? Really? Are you talking about their mothers milk or milk from the grocery store?
" soon after cats are weaned, the enzyme that enables them to digest it, lactase, begins to disappear from the gut. When an adult cat drinks milk, the indigestible lactose in its gut may start to ferment, causing a stomach upset" found this when googled "should cats drink milk?"
A lot of people think that just because cats love to eat people food that it's OK to give it to them. Cats will just about eat anything, and suffer the consequences later. Here is a good article...http://cats.about.com/od/catfoodandnutrition/f/tablescraps.htm