Amazon is not claiming to be a social network.

Social networks sell themselves to users based on what the users can share and display about themselves to their social network. The more that a user can shape his persona (by revealing different information) the more appealing a social network will be to users, a big reason why facebook is so popular is exactly for this reason: it allows you to shape your presence in a very varied way (this is why pages is a killer feature).

To describe ping, apple should have really said that its a social network for ITMS, not a social network for music.