I think that -even despite the fact that you are so close to the fire as a Samba dev- need to be dragged back into the real world yourself. The fact that some companies contribute and use some GPLv3 code for some things, does not imply GPLv3 is not preventing other companies to do the same for other things.
Example from 'the real world': I've been working as a software engineer at various companies for about 10 years now, all of them who created very specific, industrial software, all related to IC design and production. All software full of highly confidential and/or patented, non-trivial
None of what you are saying is the least bit relevant. We are talking about the reverse engineered version of someone else's file system here. This isn't the hot new arcane technology we're talking about. This is simple stuff that everyone needs to be able to share and use to communicate.
SAMBA is the perfect example of something that is outside of the core business and is so far removed from your core competitive advantage as a company, that there is no value in keeping it proprietary.
There really is ZERO value to there being any proprietary aspects associated with it.
That includes both the source code of the implementation as well as any underlying patents.
Apple simply shouldn't be doing anything that makes the GPL3 a problem.
At this point, Apple users should be scared and suspicious rather than making up all sorts of lame excuses. Of course they are not but that's another matter.
If anything, this seems to be part of a larger strategic move away from open systems. Apple has begun to focus primarily on systems that are inherently hostile to Free Software (even of the GPL2 variety).