The other way to look at it is that the phones need to be thinner to make them a reasonable size with a case on them. Cases are a consumable--mine has a ton of dings in it that otherwise the iPhone itself would've absorbed.

Or you could just not build the whole damn thing out of glass. Steel or carbon fiber can be light and thin, without the propensity to shatter into smithereens.

Most phones are a lot more durable than people seem to think, or maybe they're too lazy to take care of their expensive devices. Sure, my Moto X has a couple of battle scars, but nothing is broken.

Patina is cool and adds character.

But it lowers resale value. People don't like patina on their cars, either.

There's a lot more to life than resale value.

Not to mention, cases are for personalization.