Which is the ultimate problem of the BSD licence.

Problem with BSD license? We are discussing two separate issues here

1) Ability to unlock or root your device to run any OS

2) Having access to an open App Ecosystem.

The GNU license doesn't help with either of this issues. There are plenty of GNU/Android devices shipped with locked boot loaders. And nothing is stopping Google from locking down their App Store like Apples except a different corporate policy.

I don't think there's a problem with the BSD license, but the GNU license is actually supposed to help with those issues, just not the version used by the Linux kernel (v2).

Actually it's the only thing that has the potential to convince me to buy a product from Apple. I haven't yet but if it were closed, no way I would even consider it.

As I understand it, the BSD licence (which BTW only some elements of Mac OS X have, as happens with some elements of Windows) allows to redistribute binaries, modified or not, provided you keep the copyright notice. In that case, how are Apple products "less closed" than, say, Microsoft's?

Note: I barely use Apple or Microsoft, so the question is NOT rhetorical.

In addition to UNIXgod's comment, I can refer you to:

http://en.wikipedia.org/wiki/OS_X

There you will find:

http://en.wikipedia.org/wiki/Comparison_of_BSD_operating_sys...

"... Apple Inc.'s iOS and Mac OS X, with its Darwin base including a large amount of code derived from FreeBSD."

http://en.wikipedia.org/wiki/Darwin_(operating_system)

"Darwin is an open source POSIX-compliant computer operating system released by Apple Inc. in 2000."

Yes, Apple has used free BSD code to build an OS that is not open source. I don't think anyone would dispute that.

Referring to the Berkeley TCP/IP stack?

Indeed. How does using the stack makes windows any less closed? Since you can't even tell to which degree it was modified, I think the answer is "it doesn't at all". And I think the same reasoning goes for mac OS X.