OP: You're not entitled to a device repair or replacement if you get the device wet. All Apple is advertising is that your phone will likely continue to work normally if you accidentally splash a small amount of water on it.
As soon as you try to make a phone call in the rain, the water detectors will be triggered, and you will no longer have any right to have the device repaired under warranty. In all likelihood, the device will continue to work (by the way the 7 does not appear to have revolutionary waterproofing that the 6s didn't already have—the 6s could already withstand being submerged for extended periods while on). However, you are taking this risk knowing that the warranty cannot apply to you, nor should it, since like you said, Apple has no way of knowing what you did with the phone to get it wet.
It's really as simple as that. You should not feel entitled to anything beyond this—there is no reason to.
Apple's advertising applies to the functionality of the device, not its own liability in case of your own accident. If you want accident protection, you get AppleCare+ and pay the $100 deductible for a device replacement, same as always. With the new waterproofing features, your chances of having to pay this deductible have decreased somewhat, but Apple's liability has not.