Remember Liquipel technology? Apple bought them out last year and it was speculated that the waterproof coating would be brought to the iPhone 5. Take a look at this water test video. Why would such an amazing feature be hidden by Apple?
I agree with you, I doubt it's coated with anything. Does everyone realize what an amazing selling point waterproofing is ? If they had coated every iPhone 5 with liquipel, I'm sure they would have used it as a selling point.