[Galaxy S 4 Q&A, Help & Troubleshooting] Zaron DarkStar:
Same problem here!

Well, the exact same crack to the LED display behind the glass in the exact same place as the OP happened to me. Here are some pictures of the phone and the case it is in.

So, the events leading up to the crack are like this: I put my phone in my side pocket. I was wearing loose, soft athletic shorts so the phone had plenty of room to move and breathe. I went to my car to do some errands. Before getting in my car, I took my phone out of my pocket and placed it on the passenger side seat, so as not to accidentally squish it when I got in the car. Then I got in my car and went to the grocery store, the gas station, and the bank. Each time I got back in the car I would place the phone on the seat first. Before leaving the bank I checked if I had any new messages, and my phone was fine. Then I put my phone back on the seat and drove home. When I got home it was dark, so I opened my phone cover to use my flashlight app and it was cracked. Just like that. It has a protective shell, it was just sitting on my car seat, and it cracked...

Luckily I do have insurance, so I'll be getting it fixed.

Now I am not going to claim that this phone has a design flaw, as Samsung apparently tested this device thoroughly. http://www.youtube.com/watch?v=YA-pVRxGe8M

However, it is possible that there was a bad batch in manufacturing or something. In the end it doesn't really matter though because this result is unacceptable.

I refuse to join the ranks of consumers that blame themselves when a product does not perform as expected. Was my reasonable, cautious, average use of my phone the catalyst that caused a crack to manifest? Yes. Should I take responsibility for this hardware failure? No! Should I bite the bullet for this? Hell NO! I will be getting a free replacement or free repairs or there will be hell to pay. I should not have to wrap my phone in a blanket and carry it around on a pillow for it to survive being used!

Right here. "Fit for purpose" means that a device can easily withstand the stress of normal, average use for the function for which it was designed. For a cell phone, "normal, average use" means being carried around from place to place by the user either in their hand, a vehicle, or some form of wearable storage, while avoiding leaning directly on the phone or otherwise putting it through excessive pressure, avoid dropping it, and using it to make calls a various other electronic uses. If a phone cannot survive the basic stress of being carried around, it is not fit for purpose.

You know Barry, it sure seems like you are splitting hairs in order to defend a big company. Samsung doesn't have to publish a stress guarantee. Simply selling a device for a given functionality is an implied guarantee, and if a company doesn't treat it that way then they are in danger of running a scam, and their reputation and stock will go downhill fast. When I drop $600 on the newest high end smartphone, I expect a device that can easily withstand the stresses of average use, and maybe even the occasional abuse, while providing great functionality. If that isn't what I got, and my phone breaks, then either I will get a free replacement/repair, or I will get my money back so I can try a different product. Simple as that.