Simply disliking the lack of depth in this UI does not imply that he thinks leather stitching would be a better alternative. There is something inherently enjoyable about clicking a button with a bit of depth, even if that depth is subtle. The flat UI perspective often removes that emotional touch. Several prominent designers (@kerem and @craigmod, to name two) have emoted that adding a bit of depth to a button makes clicking it more satisfying. We are in the design business, but that involves making things more than pretty and trendy. Flat design does look beautiful, but there is a growing consensus that in many cases it also removes a bit of soul and energy from a design.