"because if the pre-giveaway clues are so obscure
that, say, 0-10% of people can answer it in the
pre-giveaway range..."
Actually, this is not terribly
obscure. Assuming that 10% of players know a clue, the
odds of one of those players being in any given room
is 1- (x*.9), where x is the number of players... so
in a room with the full complement of 8 players, the
chance of someone knowing that clue is 57% -- and that's
before adjusting for the presumable balancing of teams
to put players with a wide array of knowledge
together. Even a clue known by 5% of players will be
answered over 1/3 of the time. (Of course, this assumes
perfect recall of known questions and no sitting -- and
treats knowing and not knowing as a binary pair, whereas
in reality the question of buzzing or not buzzing is
not so clear-cut, and even a clue which NOBODY can
answer from is not necessarily worthless...)