Another possible reason some felines avoid water is that it messes with their hairdo. Cats spend a lot of time grooming themselves and each other. Take a closer look at your cat's tongue and you'll find it covered in tiny, hellish combs specially designed to remove loose hair and other debris from its coat. (Technically called "papillae," these little spines also help felines lick clean the bones of their victims, which is kind of awesome.) Now imagine you just spent the whole afternoon working on a killer perm and somebody comes along and dunks you in a tub.
In the same vein, cats come equipped with a number of glands that produce scent chemicals called pheromones. These are used for marking and communication, which is partly why they're always rubbing up against your leg. Coming into contact with water, let alone shampoo, could mess with the message they're trying to give off.
Some breeds may also be more inclined to like water from the start. If you do a quick search online, you'll find that the Turkish Van breed of domestic cats has quite a reputation for loving water. However, this cat's street cred is probably equal parts lore and fur. Turkish Vans, or "swimming cats," were said to have swam ashore from Noah's ark, apparently sick of waiting for the water to go down. More likely, the cats don't mind playing in puddles because their fur is densely cashmere-ish and water resistant.