As far as the "one shot deal" principle goes,
that is the way that most high tournaments go.
Playoffs are almost always single elimination and it is
pretty much the accepted method of determining a
champion. Single elimination adds an element of surprise to
the mix and makes for extra excitement in my opinion.
The NCAA has been taking advantage of this for years
in the annual March Madness basketball tournament. A
few years ago Arizona surprised everyone and defeated
two or three #1 seeds to win the tournament. Most
people would agree that they were far from the best team
that year, but for a couple of weeks they were the
best and had an exciting run through the tournament. I
don't see why quiz bowl should really be viewed any
differently. In high school my team lost alot of tournaments
where I felt we were the best team, but I am still a
fan of single elim.