Apple doesn't seem comfortable letting iTunes users speak directly to each other. I get the idea that they are uncomfortable allowing anything that would require moderation happen in their walled garden. And the anarchic and freewheeling nature of a vibrant social network seems somewhat counter to Apple's culture.
The part that got my attention during the keynote was that it's supposed to cover concerts as well as recorded music and media; that's a very interesting model to build a social networking application around. It's early days yet, and if Apple can recruit enough artists that can use the channel to engage their audience, and loosens up and lets people talk to each other without requiring that every single gesture they make on Ping be tied to their actions in iTunes (i.e. let regular people post comments unadorned, or even their own music and videos) it may yet become a game changer.