We've heard that Apple launched Ping without Facebook support because the two companies couldn't agree on some terms, but today AllThingsD explains that Apple actually ignored the fact that negotiations failed and incorporated Facebook's API—until Facebook blocked things.
Basically, Facebook offers open access to its wonderful friend-finding API "unless some entity wants to access it a lot. In that case, Facebook requires an agreement for reasons primarily centered on protection of Facebook user data and, of course, infrastructure impact." Considering how many iTunes users there are, Apple was definitely one of those entities who'd require an agreement with Facebook.
Unfortunately, no such agreement was reached due to what Steve Job's called "onerous terms" set forth by Facebook. You'd think that'd be the end of it, but Apple had different ideas:
Sources said Apple went ahead with a plan to access the Facebook APIs freely, but Facebook blocked it since it violated its terms of service.
When that happened, it seems Apple pulled the plug on the connection with Facebook friends.
All hope is not lost though, because according to AllThingsD's sources "the companies were still in discussions about putting the more robust Facebook Connect feature in Ping." [AllThingsD via Engadget]