If anything, I think I make an argument against it. You can make an app look like a physical address book, but I've never seen anyone use a physical address book. You could make a YouTube player that looks like a television too, but to what end? Pretty soon, people won't have seen televisions that look like anything more than a screen with a thin black bezel.

And as we move toward more unified gadgets that a lot of people have grown up with, what do we do? Make a mail client that looks like a smartphone because that's how people read mail? An eReader app that looks like a physical Kindle?

I don't think a leather address book is any more valid than a 3.5" floppy save icon. A single purpose app for contact management should reflect that it's a database of contacts, sure. Should it reflect that it's a book? Eh.