I think the GPLv3 discussion made a lot of people think twice about copyright assignment. The wikipedia exception also made people think.
The FSF promises that all licenses that they release code under will be 'in the same spirit' as the prior ones, but the GPLv3 discussion showed that what the FSF considers 'in the same spirit' is not always what the people who wrote the code consider 'in the same spirit'
Apple is doing more than is strictly required by the GPL (they could just ship the source with the binaries), so what they are doing _is_ fully compatible with the GPL.
They just aren't willing to do the copyright assignment, and the FSF has a policy to not accept any contributions that don't include such assignment, so why should Apple waste any time 'trying to get their contribution upstream' when they know that upstream will not accept it?