Not everyone gets a boner at the thought of building a PC.
Most home-builds look... well, home-built.
I can build my own but choose not to, for these and many other reasons.
So does the Calendar app in iOS > 3 use stitched leather on the iPhone? It sure doesn't do so on iOS 3.
You're right, it doesn't do so on the iPhone, it's just the iPad and Mac versions, which is interesting. My mistake. It looks like it's just the Reminders and Notes apps that share a similar design across platforms.
You could also do that by omitting the stitched leather across all three versions of the app. I'd vote for that solution instead.
You could, but the point I was making is that by sharing a design theme, it becomes more obvious that data is shared between the apps. It's essentially making the point "this is the same app". Sure you could do that without using stitched leather, but you'd need some other way of visually tying the apps together. It just happens that Apple went with stitched leather.
I think adopting a visual identity that reduces contrast can make an app less fun to use.