Rain, or even a short time at the bottom of the pool, is easily managed with a simple seal compatible with user replaceable batteries. Failure rates will be a tiny bit higher because users won't always get the closure perfect, but that's not going to affect most people. What will affect most people is an immediate two or three year extension in the life of their phones with a $15 Amazon.com order.

That's hundreds of dollars a year in savings. For me it would be about $330/yr in savings, enough to cover my streaming video and music bills completely. That savings falls in half if my time is valuable and I've got to drive to an Apple store and pay $90 for the replacement, so I've never done that. Instead, I go on Amazon.com and order an entirely new phone when my battery gets to be an issue.

I think replaceable batteries will make calculus work for me and billions of others over the long haul. Maybe 50% of consumers take advantage and save money, 49.999% never notice or care, and 0.001% miss scuba diving raw-dog with their smartphones and have to buy a specialized case for piece of mind.