My understanding was that Apple's big code dump back to WebKit/KHTML was not useful for the KDE project. Apple is following the OSS spirit in a technical sense but is not succeeding in actually working with community contributions in a meaningful way. Feel free to refute me, I have no evidence, but this was my understanding.
That was the case for the first two releases. After that the KHTML guys complained vocally (it made Slashdot) and Apple started to release diffs, then completely opened the dev process.