My neighbor has a cat that is severely obese. She is supposedly on a "diet" and has been for who knows how long. She is eleven years old and her weight problem is so bad it has caused her front legs to bow and she can't walk properly. She can sort of waddle. It is not necessary to take her to the vet because she has been like this for so long.
When my BF and I were over there one day, I pointed out that the cat was not healthy and it was not fair to her to allow her to go on like this. One of the guys that lives there said, "She's one of those Chinese cats. She's supposed to be that way."