How does the leather skin on "Find My Friends" trick people into assuming familiarity? It's an application without a physical analog, other than shouting your friends' names really loudly or wearing a weird hat or bright shirt.

I think someone with a high position in Apple's iOS app software department just really likes that leather look, and people are reading way too much into this. There are cases where the skeuomorphism is appropriate, such as the striped yellow notepad or the wooden bookshelf in iBooks, but Apple has clearly extended the use of these themes beyond where they make any kind of logical sense, making them simple arbitrary aesthetic choices.