The reason I replied wasn't so much to comment on the historical
licensing of the kernel (it's old enough to not matter much now
anyway),
but to comment on the legal argument that was the core of Linus's post
you linked to. He claimed that including the contents of GPL-2 in a
"COPYING" file with no explicit license statements had always placed
the
code under GPL v2-only. I think he's wrong. And this actually matters
for other projects. Linux is not the only project that had no explicit
license statements at some point in its history, and such an
interpretation would prevent adding per-file copyright statements with
"or later" without full contact-all-contributors relicensing - and most
projects do NOT want to be trapped at one particular version.