The story is based on a stuffed animal and its humorous death certificate and what could have happened. The point of Earl is that Earl is dead so he can't die. Being that Earl can't die you never have to worry about him like you would with a real cat so he can be a truly life long friend.
No one knows what earls life was like before he was dead mostly because he's not a real cat. This video tries to explain the sad life of earl based on the vague description.