I have mine in a thin case (made by Agent 18, but really these are cheap plastic cases you should be able to get for a couple bucks), more for the scratching than for anything else. I tend to put the phone screen side down, and without the “lip” that the case provides, I tend to get tiny little scratches on the screen.
Before I got the case, I dropped the nekkid phone without issue, and I’ve dropped it many times after, too. Wife still keeps her phone nekkid, but she’s more careful with her stuff than I am. =p
I’ve had the 3, 4, 4S and 5, and the only one that I ever broke the screen on was the 4. They’ve all been dropped multiple times, and I don’t use any protection for them. It seems to me that most drops they’ll survive fine, but if you happen to catch a corner just right, it’ll shatter.
I too have have dropped my 4S a dozen times or more (including like, four times in the last week. I wonder if I’m getting enough potassium) without incident. It’s not in a case and hasn’t been for almost a year; I did have the Apple bumpers on it for the first six months. The iPhone is not a budget product, so if you’re willing to pay the associated cost premium, why not buy the protection plan for an extra $99? If not, then there are Androids that are substantially cheaper.
My iPhone 4S fell 9" onto asphalt and hit just right (wrong) on the corner, which cracked the screen. Luckily, it’s a crack that runs across the corner, so it doesn’t really affect my use of it.
Since then, I’ve dropped it a few times from full height onto tile and cement. No damage, even though the screen is presumably weakened from the previous crack. So, they’re pretty hardy, but certainly not indestructible.
Getting a new screen from Apple is $200, and you can often get one from a 3rd party for $100, so it’s not like the whole thing is trashed if you break the screen. Given the full price of a new iPhone is $600ish, $400ish for one with a broken screen isn’t totally unreasonable.
…whereas it seems that you can smash the iPhone screen pretty much to bits and it still works fine. One of my work colleagues has an iPhone that actually has a few jagged chunks of glass missing from the top corner, and a spider’s web of cracks over most of the rest of it, and it still works. I do wonder how he avoids slicing the tips off his fingers while using it, though…