Nicely put. However, it also does not mean that the copy is
unencumbered
either, as this is not strictly stated. This is (among other things)
wiggle room.
If there is ambiguity in a contract the interpretation goes against
the party who wrote it. That is why it was essential for Microsoft
to draft this, they don't get the benefit of any wiggle room.
As a practical matter the empirical definition of law is what a
court rules. Now some complete fools get appointed to the bench
and it is impossible to be sure that there will not be a ridiculous
decision.
But consider, what is the likelihood of an adverse decision that
involves damages or an injunction prohibiting distribution against
any party that is not making a claim without granting reciprocal
rights?
If an action was taken against any party they can bring themselves
into compliance at any time. Patent disputes cost millions and there
is always a risk that the court proceedings would end with the
patent being declared invalid. Microsoft would not be in a position
to claim loss of revenue.
As a matter of longstanding IETF precedent a license with a reciprocal
rights clause is the norm. This has never been objected to in the past.
The idea of a reciprocal grant does not seem to me to be antithetical
to the aims of the GPL, quite the opposite.