But leather and metal are helpful on a camera, as is the cross hatch on the lens.
On an iPhone app cross hatching does not help you grip the control.
The leather on an iPhone app doesn't help protect against scratches or provide a superior gripping surface to polished aluminium.
If you like the idea that good design is as little design as possible then a Leica style app design isn't as little design as possible. In just the same way that a moleskin notepad app isn't helpful, nor is comic sans as a font choice despite that it approximates hand printed letters. Maybe if they really want to make the full experience the 'pen' you use to write letters can run out of ink and then you have to shake the iphone to get more ink.
Design should help the user accomplish tasks not get upvotes on dribble.
The leather and metal buttons remind me of an old camera (or one such as a Leica with a timeless design). As an example: http://i.imgur.com/EfGW5.jpg
I feel like that UI would go just fine with a camera or photo-related app.
But it totally doesn't work at all for something that I'm assuming is more along the lines of a magic 8-ball.