I have always preferred to have my iOS devices naked without a case. That because I want to feel the quality. I want to feel it as Apple wanted it to feel. So I don't want to hide the beautiful devices behind some ugly plastic cases. And I will probably never want to do that. When I had a Samsung Galaxy phone I wanted to hide the ugly plastic device behind a case though, lol :)
When the iPad Air 2 where released, I felt that it was even more necessary to have it naked without a case. I don't even want a smart cover anymore for it. And the reason is that it's very important to have it as thin and light as possible. It has replaced computers for me so I use it almost always the time. And I prefer to hold it in portrait mode and thumb type with both thumbs with all the excellent touch keyboard that are available.
And by doing so it needs to be as thin and light as possible. Otherwise it wouldn't be possible to use and hold it as long as I do.
And that is the reason why I think Apple is doing the right thing with both the iPhone and iPad, when they trying to do them as thin and light as possible. To me that is way more important than having a larger battery that would give one hour battery life more. The weight is way more important for the user experience.
And it always will for users like me that really use our devices.