The look and feel of the “naked” phone are extremely important because that is one key factor (of many) in the customer deciding to buy that phone in the first place. Nobody wants to buy an ugly phone. If look and feel didn’t matter then more people would be buying Vertu phones, arguably the most hideous in the industry.
And it is because a person likes the look and feel of the phone that he/she feels compelled to buy a case to protect it and take care of it in the first place. (And of course, people also buy cases to protect the screen from breaking when the phone is dropped.)
Replaceable batteries are not as important as you think they are. That was a legitimate concern in the 90s and early 2000s, but with the availability of chargers and sockets everywhere and the ability to charge smartphones straight from a USB cable plugged into a computer that issue is not an issue at all in the minds of users these days.
By “nothing” he means THE most successful and best selling smartphones, tablets, media boxes (Apple TV), along with THE highest customer satisfaction ratings in the industry years and years in a row. Feats that no competitor has ever come close to achieving.