Some methods of carry like zip locks or aluminum foil won't protect tinder if you get fully immersed in water, not just rained on. I'm thinking of boaters and aviators, and the kits that would be on their person. See this video at 3:40.

Phaedrus, you may have posted it before but what bags & sealing equipment are you using? The setups you've described sound great, although their performance may be improved even more if you add a bunch of smilies...