I agree. I've rarely used a case and never had a problem despite my chronic butter fingers. Getting a case always seemed like buying a Monet, wrapping it in craft paper, and putting it on the wall.
So if they've made a phone that HAS to have a case, then why not just build durability into the product?
if you look at things that are designed from the ground up not to be breakable, it has to be designed differently and it maybe ugly and a product that people won't buy because it's too bulky, etc.
Look at the Panasonic Tough book laptops, yeah i know they sell, but only to a small portion of the computer using population that requires something of that ruggedness. They are big and bulky and heavy for what power you are getting. their thinnest one is thicker than any MacBookPro you can get. Can you beef up a MacBookPro with a protective case? Yeah, what does that do? It makes it thicker, bulkier and depending on which one you buy, more expensive.
With smartphones, there are a variety of cases which protect the iPhone metal case in getting scratched/dented, and there are a variety of screen protectors that will minimize or eliminate screen cracking. You want a nice screen protector that makes your iPhone essentially shatterproof, use the NuShield (as an example), the military uses it. the thing that companies like Apple are going to do is to make it an optional add-on because there are a variety of companies making similar products and this gives you the freedom to choose.
I don't know why these people still do drop tests to see if the screen is going to crack because depending on how high they drop the product and what surface, etc., the screen will eventually crack, so all one has to do is get a screen protector which are relatively cheap and easy to apply.