The new clauses in the GPLv3 bring up legal questions that some teams would rather just not deal with, even as user space tools. As such, Apple has decided to avoid potential legal headaches and stick with tools under better understood licenses. Most of the BSDs have stuck with GPLv2 stuff, with FreeBSD actively working to replace the few bits and pieces of GPLed code in their base system with code that is under the BSD or other liberal licenses.

Nothing. Apple is just being overly paranoid or hoping to some day do things that GPLv3 won't allow them to do. Microsoft, Facebook, Google, Intel, IBM; all of these companies have some interaction with GPLv3, but Apple staunchly refuses to even touch it.

It's a real pity, because Apple's popularity is sending some message that GPLv3 is poisonous, when it reality it's only a problem for them because they chose to make it a problem for themselves.