Dr. Moglen in a January 2006 interview said: "If the kernel's terms were unambiguously GPL, which they are apparently not, (proprietary drivers) would be forbidden.".

I assume the not "unambiguous" thing is Linus's GPL personal (see the I personally believe) interpretation well known for about the last decade, that explicitly allowed to load binary only module drivers in the kernel through the EXPORT_SYMBOL interface in a few cases: like for example if the drivers were originally written for a different operative system and they were only later ported to linux in binary only form.

But now something has changed and at least one very important kernel developer says that closed source linux kernel modules are illegal, pretty much contradicting the previously well known interpretation.

Who is right and who is wrong?

I've no idea myself, the only sure thing is that they can't all be right at the same time...

If you only look at the COPYING file, then IMHO you would also have to forbid the non-GPL userland applications to call into the vsyscalls. So I previously thought the COPYING file wouldn't mean everything in the corner cases of a very special context like the operative system kernel and I thought Linus's personal interpretation meant something. But now I pretty much reassigned myself to not knowing the answer of this question, and obviously I don't really need to know the answer myself. I'm just curious to see how the people needing the answer will react to this change.