I think not every cat is lactose intolerant but most of them are.
Both my Katz (RIP) and my Luna have been raised with cow milk by their previous owners; it was so hard to make them drink water, I bought Whiskas cat milk to make them drink enough. When I got my Katz, she already had bloody diarrhea. She couldn't get rid of stomach/colon-problems all her life adn I always thought that the cow milk might have caused her problems...

Kirsten