Facebook blocked API access to Ping, Apple removed feature after launch

It comes down to money. Yes Facebook is gracious enough to allow third-parties access to its data via API, but when the third-party is as large as Apple it is going to want some money from them to cover the costs of serving up all that data.

In my opinion, Facebook has every right to ask Apple for some cash. Hopefully they can work something out and we can all move on abandoning our last.fm accounts :/