Jerry, I think your smartphone usage and carrying patterns may demonstrate the exception, not the rule, but I could again be wrong. The skinny-jean comment is targeted at a typical usage scenario for a great many. Obviously, that doesn't mean these are the only individuals who choose not to protect their phones with a case...for whatever reason.
No matter what the leading electronics manufacturers make they can't please everyone. Yet, their engineers have sound reason for their engineering choices. HTC decided to go with an aluminum closed shell...with no expansion and a sealed battery. This appeals to some. Samsung chose a plastic shell, removable battery, and upgradeable storage. This appeals to some as well. One of the the things I do appreciate about Samsung's back cover on the S4 is that you can easily find a cheap replacement for it that has all the texture some may want (Amazon) without bulking up the phone.
Sent from me LTE Note 8.0