[sjwaldron]

If you were using a decent lens filter, then getting saltwater on the front element would have never happened. Plus it adds another seal for water to get through.

[Cannikin]

I read somewhere that WR is good for light mist only.
Do the WR lenses have an O-ring at the mounting flange like the DA*`s do?.

Yes, WR lenses have an O-ring around the lens mount. The WR designation would be pretty worthless without one.

I've tested the 18-135 in moderate to somewhat heavy rain, in which I zoomed in and out frequently (the 18-135 has a double cam zoom, making it even more vulnerable). There are seals between the inner barrels. It got quite thoroughly soaked, but I could see distinct lines on the inner barrels where the water was blocked by the seals. Didn't even bother to wipe most of it off afterwards, and I found not a single droplet inside. The worst it suffered was grease on the front element from me trying to clear some of the water.

Pretty much any lens, WR or not, could easily handle "light mist". Ned Bunnell's "sweater weather" comments are rather misleading IMO. I would venture that the real difference between WR and DA* is the resistance to water pressure. WR can resist standing water sitting on the lens (from rain and such), but DA* can resist light amounts of water pressure, like say from dumping water on it as in demonstrations.

That being said, I would agree that this problem is most likely due to condensation. After you take a shower, look at the bathroom mirror. It's completely covered in condensation and water droplets, despite you (presumably) not spraying water on it. No lens design can prevent this.