Why go there with imagination when we can just observe what reality is? A smartwatch is unlike all other electronic devices. If it's got capabilities to record exercising activities, it's extremely reasonable to assume it can withstand moisture, due to sweat. If it's a watch, it's very reasonable to assume people will be outside when it may be raining, and it will get wet.
We know the manual says not to shower with it, so why risk it? It seems silly.
Even in this video where the WSJ got the Apple Watch almost 2 weeks before it officially got released, and the lady showered with it, she says Apple said not to do that.